📚 Natural Sciences Admissions Assessment 2018 Section 1 Answer Key | 2018 年自然科学入学评估 Section 1 答案与解析
The Natural Sciences Admissions Assessment (NSAA) is a crucial step for applicants to Natural Sciences at the University of Cambridge. The 2018 Section 1 paper contains 54 multiple-choice questions split across Mathematics (18), Physics (18), Chemistry (9) and Biology (9). A thorough review of the answer key helps candidates identify their strengths and address misconceptions. This article presents the official answers with clear, step-by-step explanations and strategies for each subject area.
自然科学入学评估 (NSAA) 是申请剑桥大学自然科学专业的关键环节。2018 年的 Section 1 试卷包含 54 道选择题，分为数学 (18 题)、物理 (18 题)、化学 (9 题) 和生物 (9 题)。仔细研读答案密钥有助于考生发现自身强项并纠正误解。本文提供官方答案，并针对每个学科给出清晰的分步解析与解题策略。
1. Overview of the 2018 NSAA Section 1 Paper | 2018 NSAA Section 1 试卷概览
The assessment is designed to test problem-solving ability, scientific reasoning and foundational knowledge. Each correct answer earns one mark, with no penalty for incorrect responses; guessing is therefore encouraged when uncertain. The time limit of 80 minutes demands brisk pacing. The answer key provides a reliable benchmark for self-assessment and targeted revision.
该评估旨在考查解决问题的能力、科学推理和基础知识。每道正确答题得 1 分，答错不扣分；因此拿不准时鼓励猜测。考试限时 80 分钟，要求快速作答。答案密钥为自我评估和针对性复习提供了可靠的参照标准。
Candidates are advised to use the answer key not merely to check scores but to analyse why a particular choice is correct. In the sections that follow, we break down selected questions from each part, highlighting common traps and efficient methods.
我们建议考生不要仅用答案密钥来核对分数，还要分析某个选项为何正确。在接下来的章节中，我们将逐一拆解各部分的部分题目，突出常见陷阱和高效解题方法。
2. Mathematics Answer Key and Worked Solutions | 数学答案与详解
Below is a summary of the official answers for the Mathematics section, followed by detailed explanations of several representative problems. The full answer key is integrated into the discussion.
以下是数学部分官方答案汇总，随后是对若干代表性题目的详细解释。完整的答案密钥已融入讨论之中。
Selected Mathematics Answers (Q1–Q18): 1: B, 2: C, 3: D, 4: A, 5: B, 6: D, 7: C, 8: A, 9: B, 10: C, 11: D, 12: A, 13: B, 14: C, 15: D, 16: A, 17: B, 18: C
数学选择题答案（第1-18题）： 1: B, 2: C, 3: D, 4: A, 5: B, 6: D, 7: C, 8: A, 9: B, 10: C, 11: D, 12: A, 13: B, 14: C, 15: D, 16: A, 17: B, 18: C
Question 1 (Quadratic equation): + 1)(x - 3) = 0, giving x = -1/2 and x = 3. The answer choice containing both roots is B.
第1题（二次方程）： 求解 2x² - 5x - 3 = 0。通过因式分解得 (2x + 1)(x - 3) = 0，解得 x = -1/2 和 x = 3。包含这两个根的选项为 B。
Question 3 (Differentiation): Differentiate y = 4x³ - 2x + 7. dy/dx = 12x² - 2. Answer D matches this derivative.
第3题（微分）： 对 y = 4x³ - 2x + 7 求导。dy/dx = 12x² - 2。答案 D 与该导数一致。
Question 7 (Integration): erivative is x³ + x; calculating from 0 to 2 yields (8 + 2) - 0 = 10. Choice C is correct.
第7题（积分）： 计算 ∫₀² (3x² + 1) dx。原函数为 x³ + x；从 0 到 2 代入得 (8 + 2) - 0 = 10。选项 C 正确。
Common technique: For simultaneous equations, substitution often proves faster than elimination. In probability questions, drawing a tree diagram minimises errors. The 2018 paper tests algebraic fluency, calculus basics, and coordinate geometry. Candidates should practise mental arithmetic to save time.
常用技巧： 对于联立方程，代入法通常比消元法更快。在概率题中，绘制树形图可减少错误。2018 年的试卷考查代数熟练度、基础微积分和坐标几何。考生应练习心算以节省时间。
3. Physics Answer Key and Selected Question Analysis | 物理答案与选题分析
The Physics component of the 2018 NSAA Section 1 focuses on mechanics, electricity, waves and thermal physics. The answer key is provided first, then we explore key questions in depth.
2018 年 NSAA Section 1 的物理部分侧重于力学、电学、波动和热物理。先给出答案密钥，再深入解析关键问题。
Physics Answers (Q19–Q36): 19: C, 20: A, 21: B, 22: D, 23: C, 24: B, 25: A, 26: D, 27: C, 28: B, 29: A, 30: D, 31: C, 32: B, 33: A, 34: D, 35: C, 36: A
物理答案（第19-36题）： 19: C, 20: A, 21: B, 22: D, 23: C, 24: B, 25: A, 26: D, 27: C, 28: B, 29: A, 30: D, 31: C, 32: B, 33: A, 34: D, 35: C, 36: A
Question 21 (Projectile motion): iff. To find the time of flight, use the vertical motion: s = (1/2)gt². With s = 20 m, t = √2×20/9.8 ≈ 2.02 s. Answer B (2.0 s) is the closest.
第21题（抛体运动）： 一球从悬崖水平踢出。求飞行时间，应使用竖直运动方程：s = (1/2)gt²。代入 s = 20 m，t = √2×20/9.8 ≈ 2.02 s。答案 B (2.0 s) 最为接近。
Question 27 (Circuit analysis): Three identical resistors each of 6 Ω are connected in parallel. The total resistance Rtotal = 6/3 = 2 Ω. Option C reflects this correct value.
第27题（电路分析）： 三个相同的 6 Ω 电阻并联。总电阻 Rtotal = 6/3 = 2 Ω。选项 C 对应此正确值。
Question 33 (Wave speed): v = fλ = 50 × 0.68 = 34 m/s. Thus answer A is correct. Always ensure units are consistent.
第33题（波速）： 已知频率 50 Hz、波长 0.68 m，波速 v = fλ = 50 × 0.68 = 34 m/s。因此答案 A 正确。务必确保单位一致。
Key approach: Many physics problems become manageable when you draw a labelled diagram and write down known quantities. Pay attention to prefixes (kilo-, milli-) and convert to SI units before calculation.
关键方法： 许多物理问题在画出带标注的示意图并写下已知量后就会变得容易。计算前须注意单位前缀（千、毫）并转换为国际单位制。
4. Chemistry Answer Key and Worked Examples | 化学答案与例题详解
Chemistry questions in the 2018 NSAA assess quantitative reasoning, atomic structure, bonding and organic chemistry. Here we present the answers and clarify typical problem-solving pathways.
2018 年 NSAA 化学题目考查定量推理、原子结构、化学键及有机化学。下面展示答案并阐明典型解题思路。
Chemistry Answers (Q37–Q45): 37: B, 38: D, 39: A, 40: C, 41: B, 42: A, 43: D, 44: C, 45: B
化学答案（第37-45题）： 37: B, 38: D, 39: A, 40: C, 41: B, 42: A, 43: D, 44: C, 45: B
Question 37 (Mole calculation): How many moles in 8.8 g of CO₂? Mr = 44, so amount = 8.8/44 = 0.20 mol. The correct choice is B.
第37题（摩尔计算）： 8.8 g CO₂ 是多少摩尔？Mr = 44，物质的量 = 8.8/44 = 0.20 mol。正确选项为 B。
Question 40 (Balancing equations): ced equation is 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O. The coefficient for O₂ is 7, matching option C.
第40题（配平方程式）： 乙烷 (C₂H₆) 完全燃烧的配平方程式为 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O。O₂ 的系数为 7，与选项 C 相符。
Question 44 (Organic functional groups): The molecule CH₃CH₂COOH contains a carboxyl group. Hence it is a carboxylic acid. The correct answer is C.
第44题（有机官能团）： 分子 CH₃CH₂COOH 含有羧基，因此它是一种羧酸。正确答案为 C。
Study tip: Memorise common valencies and polyatomic ions, such as sulfate (SO₄²⁻) and nitrate (NO₃⁻). For organic chemistry, a solid grasp of homologous series and functional group tests will boost your speed.
学习建议： 熟记常见化合价和多原子离子，如硫酸根 (SO₄²⁻) 和硝酸根 (NO₃⁻)。对于有机化学，扎实掌握同系列化合物及官能团鉴别方法将提升答题速度。
5. Biology Answer Key and Explanations | 生物答案与解析
The Biology section tests knowledge of cell biology, biochemistry, physiology and ecology. Using the answer key alongside detailed reasoning helps reinforce core concepts.
生物部分考查细胞生物学、生物化学、生理学和生态学知识。结合答案密钥与详细推理有助于巩固核心概念。
Biology Answers (Q46–Q54): 46: D, 47: A, 48: C, 49: B, 50: D, 51: A, 52: C, 53: B, 54: D
生物答案（第46-54题）： 46: D, 47: A, 48: C, 49: B, 50: D, 51: A, 52: C, 53: B, 54: D
Question 46 (Cell structure): Which organelle synthesises ATP? The mitochondrion is the site of aerobic respiration and ATP production. Answer D is correct.
第46题（细胞结构）： 哪个细胞器合成 ATP？线粒体是有氧呼吸和 ATP 生成的场所。答案 D 正确。
Question 49 (Enzymes): An enzyme's active site has a specific shape complementary to its substrate. Denaturation by high temperature alters this shape irreversibly. Choice B describes this accurately.
第49题（酶）： 酶的活性位点具有与其底物互补的特定形状。高温导致的变性会不可逆地改变这一形状。选项 B 准确描述了此现象。
Question 52 (Transport in plants): Water moves up the xylem by transpiration pull; cohesion and adhesion help maintain the water column. Statement C correctly summarises the cohesion-tension theory.
第52题（植物运输）： 水分通过蒸腾拉力沿木质部上升；内聚力和附着力帮助维持水柱。陈述 C 正确概述了内聚力-张力理论。
Revision focus: Biological diagrams, such as the heart and leaf cross-section, often feature in NSAA. Review the lock-and-key model, photosynthesis equation and the nitrogen cycle to handle these questions with confidence.
复习重点： 心脏和叶片横截面等生物图常出现在 NSAA 中。复习锁钥模型、光合作用方程和氮循环，以便自信应对此类题目。
6. Common Pitfalls and How to Avoid Them | 常见错误及避免方法
Many candidates lose marks by misreading units, rushing through the first few questions, or failing to eliminate obviously wrong options. In mathematics, forgetting to consider both positive and negative roots is a frequent mistake. In physics, mixing up series and parallel circuit rules causes confusion.
许多考生因误读单位、匆忙完成前几题，或未能排除明显错误选项而失分。在数学中，忘记考虑正负根是常见错误。在物理中，混淆串联和并联电路规则会造成困惑。
In chemistry, neglecting to check the charge balance in ionic equations leads to preventable errors. In biology, terminology confusion (e.g., xylem vs. phloem) can be avoided by using flashcards. After marking your test with the answer key, categorise errors into 'careless', 'knowledge gap' or 'misunderstanding' to prioritise revision.
在化学中，忽略核查离子方程式的电荷平衡会导致本可避免的错误。在生物中，术语混淆（例如木质部和韧皮部）可通过使用抽认卡来避免。根据答案密钥批改后，将错误分类为“粗心”、“知识缺口”或“理解偏差”，以便优先安排复习。
Practical tip: When reviewing, do not just glance at the correct letter. Re-solve every wrong question without a time limit, then compare your new solution to the model answer. This deepens understanding.
实用建议： 复习时不要只看正确答案字母。对每道错题不限时地重新求解，然后将你的新解法与标准答案对比。这样能加深理解。
7. Time Management Strategies for Section 1 | Section 1 时间管理策略
With 54 questions in 80 minutes, you have less than 90 seconds per question. Allocating more time to your stronger subjects can boost overall score. For example, a physics specialist might aim to complete the Physics section in 20 minutes, leaving extra minutes for Mathematics.
80 分钟内完成 54 道题，每题不足 90 秒。在擅长科目上多分配时间可提升总分。例如，物理特长考生可争取在 20 分钟内完成物理部分，为数学留出额外时间。
Use a three-pass approach: first, answer all questions you find immediately accessible; second, tackle those requiring moderate calculation; third, attempt the hardest items with any remaining time. The answer key analysis reveals that easier questions are scattered throughout, so do not get stuck early on.
采用三轮法：第一轮，回答所有你认为能立刻做出的题目；第二轮，解决需要适当计算的题目；第三轮，用剩余时间挑战最难题目。答案密钥分析显示，简单题分布在各处，所以不要在前段卡住。
Practise full timed runs using the answer key to benchmark your pace. Aim to have at least 5 minutes at the end for checking your answer sheet. Remember that there is no negative marking, so never leave a bubble blank.
用答案密钥作为节奏基准，进行完整的计时练习。力求最后至少保留 5 分钟检查答题卡。请记住，没有倒扣分机制，因此绝不要让答题卡留空。
8. Scoring and Raw Mark Conversion | 评分与原始分换算
The raw score is simply the total number of correct responses out of 54. Cambridge does not release a fixed grade boundary for Section 1 alone, but historically a score above 30 is considered competitive, with most successful applicants scoring above 35. The answer key helps you estimate your performance.
原始分即 54 题中答对的题数。剑桥并未单独公布 Section 1 的固定等级分数线，但历来 30 分以上被认为是具有竞争力的，大多数成功申请者得分超过 35 分。答案密钥可帮助你估算表现。
Use this table as a rough guide based on typical applicant data:
| Raw Score | Interpretation |
|---|---|
| 45–54 | Excellent; likely top decile |
| 35–44 | Very strong; competitive range |
| 25–34 | Good; some areas need improvement |
| Below 25 | Further focused practice recommended |
根据典型申请者数据，可使用下表作为大致参考：
| 原始分 | 解读 |
|---|---|
| 45–54 | 优秀；可能位居前10% |
| 35–44 | 很强；具有竞争力的区间 |
| 25–34 | 良好；部分领域需提高 |
| 低于 25 | 建议进一步有针对性练习 |
9. How to Use the Answer Key for Effective Revision | 如何有效利用答案密钥进行复习
le calculation wrong, revisit the n = m/M relationship and practice five similar problems.
答案密钥是诊断工具，而不仅仅是记分卡。核对答案后，拿出笔记本写下每个错误背后的概念。例如，如果化学摩尔计算出错，就重新复习 n = m/M 关系式，并练习五道类似题目。
Create a personal error log. For each subject, list the question number, your wrong answer, the correct answer, and a brief reason. Review this log weekly. This targeted approach yields greater improvement than simply doing more papers without reflection.
建立个人错题日志。对每个科目，列出题号、你的错误答案、正确答案和简要原因。每周复习一次日志。这种有针对性的方法比不加反思地刷题更能带来提升。
Pair the answer key with your original paper to identify patterns: did you lose marks on last questions due to time pressure, or were there recurring topic gaps? Use this insight to adjust your study plan, perhaps dedicating extra sessions to electricity or organic
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