📚 Year 9 CIE Computer Science: Core Knowledge Review | Year 9 CIE 计算机：核心知识点梳理
This comprehensive guide covers the essential topics for Year 9 students following the Cambridge (CIE) Computer Science curriculum. We will break down core concepts such as hardware, software, data representation, programming, networks, cybersecurity, and the system life cycle. Each section is designed to reinforce your understanding and help you prepare for assessments with clear explanations and practical examples.
本综合指南涵盖了剑桥（CIE）计算机科学课程中 9 年级学生必须掌握的核心主题。我们将分解硬件、软件、数据表示、编程、网络、网络安全和系统生命周期等核心概念。每一节都旨在巩固你的理解，并通过清晰的解释和实际示例帮助你为评估做好准备。
1. Introduction to Computer Systems | 计算机系统导论
A computer system is an electronic device that takes input, processes it, stores data, and produces output. The fundamental model is the Input-Process-Output (IPO) model. Input can come from a keyboard, mouse, microphone, or sensor; processing is carried out by the CPU; output may be displayed on a screen, printed, or played through speakers. Storage holds data and programs both temporarily and permanently.
计算机系统是一种电子设备，它接收输入、进行处理、存储数据并产生输出。基本模型是“输入-处理-输出”（IPO）模型。输入可以来自键盘、鼠标、麦克风或传感器；处理由 CPU 执行；输出可以显示在屏幕上、打印出来或通过扬声器播放。存储器用于暂时和永久地保存数据和程序。
Embedded systems are specialised computers built into larger devices like washing machines, cars, and digital watches. They are dedicated to a single task, which makes them efficient and reliable. General-purpose computers, such as desktops and laptops, can run many different applications and are more flexible.
嵌入式系统是内置于洗衣机、汽车和电子手表等大型设备中的专用计算机。它们专用于单一任务，因此高效且可靠。通用计算机（如台式机和笔记本电脑）可以运行多种不同的应用程序，更加灵活。
The key components of a computer system are connected via buses: the data bus, address bus, and control bus. These pathways allow communication between the processor, memory, and input/output devices. Understanding the IPO model is the first step in mastering computer science.
计算机系统的关键组件通过总线连接：数据总线、地址总线和控制总线。这些通道允许处理器、存储器和输入/输出设备之间进行通信。理解 IPO 模型是掌握计算机科学的第一步。
2. Hardware Components | 硬件组成
The Central Processing Unit (CPU) is often called the 'brain' of the computer. It consists of the Control Unit (CU), which directs operations; the Arithmetic Logic Unit (ALU), which performs calculations and logical comparisons; and registers, which are small, fast storage locations. The CPU fetches, decodes, and executes instructions in a continuous cycle.
中央处理器（CPU）常被称为计算机的“大脑”。它由控制单元（CU，指挥操作）、算术逻辑单元（ALU，执行计算和逻辑比较）以及寄存器（小型、快速的存储位置）组成。CPU 在一个连续的周期中取指、解码和执行指令。
Primary memory includes Random Access Memory (RAM) and Read-Only Memory (ROM). RAM is volatile – its contents are lost when power is switched off – and it holds the data and programs currently in use. ROM is non-volatile and contains firmware, such as the BIOS, which is needed to start the computer.
主存储器包括随机存取存储器（RAM）和只读存储器（ROM）。RAM 是易失性的——断电后其内容会丢失——它保存着当前正在使用的数据和程序。ROM 是非易失性的，包含固件，例如启动计算机所需的 BIOS。
Secondary storage devices, like Hard Disk Drives (HDDs), Solid-State Drives (SSDs), USB flash drives, and optical discs, provide long-term storage. SSDs are faster and more durable than HDDs because they have no moving parts, but they are typically more expensive per gigabyte.
辅助存储设备，如硬盘驱动器（HDD）、固态硬盘（SSD）、USB 闪存驱动器和光盘，提供长期存储。SSD 比 HDD 更快、更耐用，因为它们没有移动部件，但通常每 GB 价格更高。
Input devices (keyboard, mouse, touchscreen) send data into the computer. Output devices (monitor, printer, speakers) display or present the results. Understanding how these hardware pieces interact helps in diagnosing basic faults and upgrading systems.
输入设备（键盘、鼠标、触摸屏）将数据送入计算机。输出设备（显示器、打印机、扬声器）显示或呈现结果。了解这些硬件如何相互作用有助于诊断基本故障和升级系统。
3. Software and Operating Systems | 软件与操作系统
Software is divided into two main categories: system software and application software. System software includes the operating system (OS) and utility programs; it manages hardware and provides a platform for running applications. Application software lets users perform specific tasks, such as word processing, web browsing, or gaming.
软件主要分为两类：系统软件和应用软件。系统软件包括操作系统（OS）和实用程序；它管理硬件并为应用程序提供运行平台。应用软件让用户执行特定任务，如文字处理、网页浏览或游戏。
The operating system performs several critical functions: managing memory (allocating RAM to programs), handling file management (organising, saving, deleting files), providing a user interface (graphical or command-line), managing peripheral devices through drivers, and ensuring security with user accounts and access controls.
操作系统执行若干关键功能：管理内存（为程序分配 RAM）、处理文件管理（组织、保存、删除文件）、提供用户界面（图形或命令行）、通过驱动程序管理外围设备，以及通过用户账户和访问控制确保安全。
Common operating systems include Microsoft Windows, macOS, Linux, iOS, and Android. Each has its strengths and is suited to different hardware platforms. Utility software includes antivirus programs, disk defragmenters, backup tools, and compression software, all of which help maintain the system's performance and security.
常见的操作系统包括 Microsoft Windows、macOS、Linux、iOS 和 Android。每种系统都有其优势，并适用于不同的硬件平台。实用软件包括杀毒程序、磁盘碎片整理程序、备份工具和压缩软件，它们都有助于维护系统的性能和安全。
Open-source software is a concept where the source code is available for anyone to inspect, modify, and distribute. Proprietary software is owned by a company and its code is kept secret. Both models have advantages regarding cost, support, and customisability.
开源软件是一个概念，其源代码可供任何人检查、修改和分发。专有软件归公司所有，其代码保密。两种模式在成本、支持和可定制性方面各有优势。
4. Data Representation | 数据表示
Computers use binary (base-2) because they rely on two states: on (1) and off (0). All data – numbers, text, images, sound – is ultimately stored as sequences of 0s and 1s. A single binary digit is called a bit. A group of 8 bits is a byte, which can represent 256 different values.
计算机使用二进制（基数为 2），因为它们依赖两种状态：开（1）和关（0）。所有数据——数字、文本、图像、声音——最终都以 0 和 1 的序列存储。单个二进制数字称为位（bit）。8 位组成一个字节（byte），可以表示 256 种不同的值。
× 2⁰) = 8 + 4 + 0 + 1 = 13. To convert decimal to binary, repeatedly divide the number by 2 and record the remainders.
要将二进制数转换为十进制，将每一位乘以相应的 2 的幂。例如，二进制 1101 等于 (1 × 2³) + (1 × 2²) + (0 × 2¹) + (1 × 2⁰) = 8 + 4 + 0 + 1 = 13。要将十进制转换为二进制，反复将数字除以 2 并记录余数。
for binary because one hex digit represents exactly four bits (a nibble). The digits are 0–9 and A–F, where A = 10, B = 11, up to F = 15. Hex is commonly seen in colour codes (e.g., #FF5733) and memory addresses.
十六进制（基数为 16）用作二进制的简写，因为一位十六进制数字正好表示四位二进制位（半个字节）。数字为 0–9 和 A–F，其中 A = 10，B = 11，直至 F = 15。十六进制常见于颜色代码（例如 #FF5733）和内存地址。
Text is represented using character sets such as ASCII (American Standard Code for Information Interchange), which uses 7 bits to represent 128 characters, and Unicode, which supports a vast range of characters from many writing systems and emojis. Images are stored as a grid of pixels, each represented by a binary code for colour. Sound is stored by sampling the sound wave many times per second and converting each sample to a binary number.
文本使用字符集表示，如 ASCII（美国信息交换标准代码）使用 7 位表示 128 个字符，而 Unicode 支持众多书写系统和表情符号。图像存储为像素网格，每个像素用颜色的二进制代码表示。声音则通过对声波进行每秒多次采样并将每个采样转换为二进制数字来存储。
Number of colours = 2ⁿ, where n is the colour depth in bits.
颜色数 = 2ⁿ，其中 n 为颜色深度（位）。
5. Programming Basics | 编程基础
Programming involves writing instructions for a computer to execute. The three fundamental programming constructs are Sequence, Selection, and Iteration. Sequence means executing instructions in order, one after another. Selection means making decisions based on conditions (e.g., IF-THEN-ELSE). Iteration means repeating a block of code (loops like FOR, WHILE).
编程涉及编写计算机要执行的指令。三种基本的编程结构是顺序、选择和迭代。顺序意味着按顺序依次执行指令。选择意味着根据条件做出决策（例如 IF-THEN-ELSE）。迭代意味着重复一段代码（循环，如 FOR、WHILE）。
Variables are named storage locations that hold data which can change while a program runs. Each variable has an identifier, a data type, and a value. Common data types include integer (whole numbers), float (decimal numbers), string (text), and Boolean (True/False). Constants are similar to variables but their values cannot be changed after they are set.
变量是命名的存储位置，用于保存程序运行过程中可以更改的数据。每个变量都有一个标识符、一个数据类型和一个值。常见的数据类型包括整数（整数）、浮点数（小数）、字符串（文本）和布尔值（真/假）。常量与变量类似，但其值在设置后无法更改。
thmetic operators include +, -, *, /, and MOD (remainder). Comparison operators (>, <, ==, ! pressions. Understanding these basics is essential before moving on to writing algorithms.
运算符是对数据执行操作的符号。算术运算符包括 +、-、*、/ 和 MOD（取余）。比较运算符（>、<、==、!=）用于比较值。逻辑运算符（AND、OR、NOT）用于组合布尔表达式。在继续编写算法之前，理解这些基础知识至关重要。
Programs must be written in a programming language, such as Python, Scratch, or Java. High-level languages are closer to human language and must be translated into machine code by a compiler or interpreter. Syntax errors occur when the rules of the language are broken; logic errors happen when the program runs but produces incorrect results.
程序必须以编程语言编写，例如 Python、Scratch 或 Java。高级语言更接近人类语言，必须由编译器或解释器翻译成机器代码。语法错误发生在违反语言规则时；逻辑错误发生在程序运行但产生不正确结果时。
6. Algorithms and Flowcharts | 算法与流程图
An algorithm is a step-by-step procedure to solve a problem. It must be precise, finite, and unambiguous. Algorithms can be expressed in pseudocode (structured English that resembles code but is easy to read) or drawn as flowcharts. Common algorithms include searching (linear search, binary search) and sorting (bubble sort, insertion sort).
算法是解决问题的分步过程。它必须精确、有限且不含糊。算法可以用伪代码（类似于代码但易于阅读的结构化英语）表示，也可以绘制为流程图。常见的算法包括搜索（线性搜索、二分搜索）和排序（冒泡排序、插入排序）。
Flowcharts use standard symbols: an oval for start/end, a rectangle for a process, a diamond for a decision, and arrows to show the flow. Tracing through a flowchart manually helps to verify the logic and find errors. Dry running means stepping through the code or algorithm by hand, recording variable changes in a trace table.
流程图使用标准符号：椭圆表示开始/结束，矩形表示处理步骤，菱形表示决策，箭头表示流程。手动追踪流程图有助于验证逻辑并发现错误。干运行（dry run）指手动逐步执行代码或算法，在跟踪表中记录变量变化。
Linear search checks each element in a list one by one until the target is found or the end is reached. It works on unsorted lists and has a worst-case time complexity of O(n). Binary search requires the list to be sorted; it repeatedly divides the search interval in half, achieving O(log n) time. Understanding these differences helps in selecting the most efficient algorithm.
线性搜索逐个检查列表中的每个元素，直到找到目标或到达末尾。它适用于未排序的列表，最坏情况时间复杂度为 O(n)。二分搜索要求列表已排序；它反复将搜索间隔减半，时间复杂度为 O(log n)。理解这些差异有助于选择最有效的算法。
Bubble sort compares adjacent elements and swaps them if they are in the wrong order, repeating until no swaps are needed. Insertion sort builds the final sorted list one item at a time, shifting elements as necessary. Knowing how to trace and implement these algorithms is a key practical skill in computer science.
冒泡排序比较相邻元素，如果顺序错误则交换它们，重复直到不需要交换为止。插入排序一次构建一个已排序的最终列表，根据需要移动元素。知道如何追踪和实现这些算法是计算机科学中的一项关键实践技能。
7. Computer Networks | 计算机网络
A computer network connects two or more devices to share data and resources. Networks can be classified by scale: a Local Area Network (LAN) covers a small geographic area like a school or office; a Wide Area Network (WAN) spans large distances, often connecting multiple LANs (the Internet is the largest WAN).
计算机网络将两个或多个设备连接起来以共享数据和资源。网络可按规模分类：局域网（LAN）覆盖学校或办公室等小型地理区域；广域网（WAN）跨越长距离，通常连接多个局域网（互联网是最大的广域网）。
Network hardware includes switches, which connect devices within a LAN and forward data to the correct device using MAC addresses; routers, which connect different networks and direct data packets using IP addresses; and Network Interface Cards (NICs), which provide the physical connection. Cabling (Ethernet) and wireless (Wi-Fi) are the main transmission media.
网络硬件包括交换机（在局域网内连接设备并使用 MAC 地址将数据转发到正确设备）、路由器（连接不同网络并使用 IP 地址引导数据包）和网络接口卡（NIC，提供物理连接）。布线（以太网）和无线（Wi-Fi）是主要的传输介质。
Data is broken into packets for transmission. Each packet contains a header (with source and destination IP addresses, sequence number) and payload (the actual data). Packets may travel by different routes and are reassembled at the destination. Key protocols include TCP/IP (Transmission Control Protocol/Internet Protocol), which ensures reliable delivery, and HTTP/HTTPS for web traffic.
数据被分割成数据包进行传输。每个数据包包含头部（带有源和目标 IP 地址、序列号）和有效载荷（实际数据）。数据包可能通过不同路由传输，在目的地重新组装。关键协议包括 TCP/IP（传输控制协议/互联网协议，确保可靠交付）和用于网络流量的 HTTP/HTTPS。
The Domain Name System (DNS) translates human-readable domain names (like www.example.com) into IP addresses that computers understand. Without DNS, users would have to remember numerical IP addresses. Firewalls monitor and control incoming and outgoing network traffic based on security rules, protecting the network from unauthorised access.
域名系统（DNS）将人类可读的域名（如 www.example.com）翻译成计算机能理解的 IP 地址。没有 DNS，用户将不得不记住数字 IP 地址。防火墙根据安全规则监控和控制传入和传出的网络流量，保护网络免受未经授权的访问。
8. Cybersecurity and Online Safety | 网络安全与在线安全
Cybersecurity involves protecting computer systems, networks, and data from digital attacks. Threats include malware (viruses, worms, ransomware), phishing (fraudulent emails or websites that trick users into revealing personal information), and social engineering (manipulating people into breaking security procedures). Denial-of-Service (DoS) attacks flood a system with traffic to make it unavailable.
网络安全涉及保护计算机系统、网络和数据免受数字攻击。威胁包括恶意软件（病毒、蠕虫、勒索软件）、网络钓鱼（欺骗用户泄露个人信息的欺诈性电子邮件或网站）和社会工程（操纵人们违反安全程序）。拒绝服务（DoS）攻击用流量淹没系统使其不可用。
Protection methods include using strong, unique passwords; enabling two-factor authentication (2FA); keeping software and operating systems updated with security patches; installing and updating antivirus and anti-malware software; and being cautious about clicking links or downloading attachments from unknown sources.
保护方法包括使用强而独特的密码；启用双因素认证（2FA）；保持软件和操作系统更新安全补丁；安装并更新杀毒和反恶意软件；谨慎点击不明来源的链接或下载附件。
Encryption is the process of converting plaintext into ciphertext using an algorithm and a key, making the data unreadable without the correct key. This protects data in transit (e.g., HTTPS uses encryption) and at rest (e.g., encrypted hard drives). Symmetric encryption uses the same key for encryption and decryption; asymmetric encryption uses a public and a private key pair.
加密是使用算法和密钥将明文转换为密文的过程，没有正确的密钥数据就无法读取。这可以保护传输中的数据（例如 HTTPS 使用加密）和静态数据（例如加密硬盘）。对称加密使用相同的密钥进行加密和解密；非对称加密使用公钥和私钥对。
Online safety for students includes protecting personal information, recognising cyberbullying, and understanding the long-term impact of a digital footprint. Always think before you post, use privacy settings on social media, and report any suspicious or harmful behaviour to a trusted adult.
学生的在线安全包括保护个人信息、识别网络欺凌以及理解数字足迹的长期影响。务必在发布前思考，使用社交媒体的隐私设置，并向可信赖的成年人报告任何可疑或有害行为。
9. The System Life Cycle | 系统生命周期
The system life cycle is a structured approach to developing new computer systems or maintaining existing ones. The stages commonly include: Analysis, Design, Development/Implementation, Testing, Deployment, and Maintenance. Each stage has specific deliverables and reviews to ensure the final system meets the user's needs.
系统生命周期是开发新计算机系统或维护现有系统的结构化方法。阶段通常包括：分析、设计、开发/实施、测试、部署和维护。每个阶段都有特定的交付成果和审查，以确保最终系统满足用户需求。
During analysis, the problem is clearly defined, and feasibility studies are conducted. Data gathering techniques include interviews, questionnaires, observation, and examining existing documentation. The output is a requirements specification document agreed upon with the stakeholders. Design involves planning the system architecture, user interface, data structures, and security measures.
在分析阶段，明确问题并进行可行性研究。数据收集技术包括访谈、问卷调查、观察和检查现有文档。输出是与利益相关者商定的需求规格文档。设计阶段涉及规划系统架构、用户界面、数据结构和安全措施。
Development (or implementation) is where the actual coding or system configuration takes place. After development, testing is crucial. Tests include unit testing (individual modules), integration testing (combined modules), system testing (the complete system), and acceptance testing (by the client). Bugs are recorded, fixed, and retested.
开发（或实施）阶段是实际编码或系统配置的地方。开发后，测试至关重要。测试包括单元测试（单个模块）、集成测试（组合模块）、系统测试（整个系统）和验收测试（由客户进行）。错误被记录、修复并重新测试。
Deployment means installing the system and training users. This may be done as a direct changeover (risky), parallel running (old and new run together), phased rollout, or pilot running. Maintenance continues after deployment: corrective (fixing bugs), adaptive (changing to meet new requirements), and perfective (improving performance). Understanding this cycle is essential for any software project.
部署意味着安装系统并培训用户。可以采用直接转换（有风险）、并行运行（新旧系统一起运行）、分阶段推出或试运行等方式。部署后维护继续：纠正性（修复错误）、适应性（改变以满足新要求）和完善性（提高性能）。理解这个周期对任何软件项目都至关重要。
10. Emerging Technologies and Ethics | 新兴技术与伦理
Emerging technologies like Artificial Intelligence (AI), the Internet of Things (IoT), blockchain, and quantum computing are reshaping the world. AI enables machines to learn from data and make decisions. IoT connects everyday objects to the Internet, allowing them to send and receive data. These technologies raise important ethical questions.
人工智能（AI）、物联网（IoT）、区块链和量子计算等新兴技术正在重塑世界。AI 使机器能够从数据中学习并做出决策。IoT 将日常物品连接到互联网，使它们能够发送和接收数据。这些技术引发了重要的伦理问题。
Ethical considerations in computing include data privacy, algorithmic bias, and the digital divide. Data privacy concerns how personal information is collected, stored, and used. Algorithmic bias occurs when AI systems produce unfair outcomes due to biased training data or design. The digital divide refers to the gap between those who have access to technology and those who do not.
计算机领域的伦理考量包括数据隐私、算法偏见和数字鸿沟。数据隐私关注个人信息如何被收集、存储和使用。算法偏见指 AI 系统因有偏见的训练数据或设计而产生不公平的结果。数字鸿沟指的是能够获取技术的人与无法获取技术的人之间的差距。
Legal frameworks such as the Data Protection Act (DPA) and the General Data Protection Regulation (GDPR) set rules for handling personal data. They grant individuals rights over their data and require organisations to be transparent about its use. Plagiarism and copyright infringement are also important topics: always credit sources and use licensed or original material.
法律框架如《数据保护法》（DPA）和《通用数据保护条例》（GDPR）为处理个人数据制定了规则。它们赋予个人对其数据的权利，并要求组织在使用数据时保持透明。抄袭和侵犯版权也是重要话题：始终注明出处并使用经许可或原创的材料。
As computer scientists, students must consider the social impact of technology. This includes how automation may affect employment, the environmental impact of data centres, and the responsibility to design inclusive, accessible systems that do not discriminate.
作为计算机科学的学习者，学生必须考虑技术的社会影响。这包括自动化如何影响就业、数据中心对环境的影响，以及设计包容、可访问且不歧视的系统的责任。
11. Data Handling and Databases | 数据处理与数据库
Databases organise data so it can be easily accessed, managed, and updated. A relational database stores data in tables that are linked by primary and foreign keys. Each table is made up of rows (records) and columns (fields). Key concepts include atomicity of data, reducing redundancy, and maintaining integrity.
数据库对数据进行组织，以便于访问、管理和更新。关系数据库将数据存储在用主键和外键链接的表中。每个表由行（记录）和列（字段）组成。关键概念包括数据原子性、减少冗余和保持完整性。
rd language. A typical SELECT query might be: SELECT name, age FROM students WHERE grade = 'A' specific data meeting the condition. Other operations include INSERT, UPDATE, and DELETE.
查询用于从数据库中提取信息。结构化查询语言（SQL）是标准语言。一个典型的 SELECT 查询可能是：SELECT name, age FROM students WHERE grade = 'A'; 这将检索满足条件的特定数据。其他操作包括 INSERT、UPDATE 和 DELETE。
Flat-file databases store all data in a single table, which can lead to duplication and inconsistency. Relational databases overcome this by splitting data into related tables, reducing redundancy with a process called normalisation. Understanding relationships (one-to-one, one-to-many, many-to-many) is vital for good database design.
平面文件数据库将所有数据存储在一个表中，这可能导致重复和不一致。关系数据库通过将数据拆分到相关表中来克服这一问题，通过称为规范化的过程减少冗余。理解关系（一对一、一对多、多对多）对于良好的数据库设计至关重要。
Data can be validated (checking if data is reasonable) and verified (checking if data is correct). Validation rules include range checks, format checks, and presence checks. Verification might involve double entry (typing data twice) or visual checks. These techniques maintain data quality.
数据可以验证（检查数据是否合理）和核实（检查数据是否正确）。验证规则包括范围检查、格式检查和存在性检查。核实可能涉及双重录入（数据输入两次）或目视检查。这些技术维护数据质量。
12. Computational Thinking and Problem Solving | 计算思维与问题解决
Computational thinking is a problem-solving approach that includes decomposition (breaking down a problem into smaller parts), pattern recognition (identifying similarities), abstraction (focusing on important information and ignoring irrelevant details), and algorithm design (creating step-by-step solutions). These skills apply not only to computing but to many real-world situations.
计算思维是一种问题解决方法，包括分解（将问题分解为更小的部分）、模式识别（识别相似性）、抽象（关注重要信息并忽略无关细节）和算法设计（创建分步解决方案）。这些技能不仅适用于计算机领域，也适用于许多实际情境。
When faced with a programming challenge, start by clearly understanding the problem. Break it down into manageable tasks, think of similar problems you have solved before, and then devise a logical sequence of steps. Testing and debugging are natural parts of the process – every error is an opportunity to learn.
面对编程挑战时，首先要清晰地理解问题。将其分解为可管理的任务，想想你以前解决过的类似问题，然后设计一个逻辑步骤序列。测试和调试是这个过程的自然组成部分——每个错误都是一个学习的机会。
Tools such as trace tables help to simulate how a program will execute by tracking the changing values of variables. This is extremely useful for identifying off-by-one errors and logic flaws. Practising with puzzles and simple coding tasks develops these computational thinking muscles over time.
像跟踪表这样的工具通过跟踪变量的变化值来模拟程序的执行方式。这对于识别差一错误和逻辑缺陷非常有用。长期坚持通过解谜和简单的编码任务练习，可以锻炼这些计算思维能力。
Ultimately, Year 9 students should aim to become confident in writing, understanding, and debugging small programs. They should be able to explain how data is represented, how hardware and software work together, and how networks function. With this solid foundation, they will be well-prepared for the challenges of IGCSE and beyond.
最终，9 年级学生应以自信地编写、理解和调试小型程序为目标。他们应能够解释数据如何表示、硬件和软件如何协同工作以及网络如何运行。有了这个坚实的基础，他们将为进一步学习 IGCSE 及更高阶段的挑战做好充分准备。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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