📚 AS Edexcel Engineering: Essay Writing Framework and Sample Essays | AS Edexcel 工程：论文写作框架与范文
Mastering extended-response questions in AS Edexcel Engineering requires more than just technical knowledge; it demands a clear, logical structure that guides the examiner through your reasoning. This article provides a proven framework for constructing high-scoring essays and includes annotated sample essays covering materials, mechanical systems and electronics. Use these strategies to transform your jumbled thoughts into coherent, examiner-friendly responses.
在 AS Edexcel 工程考试中掌握拓展答题并不只需要技术知识，还需要一个清晰、逻辑严谨的结构来引导考官理解你的推理过程。本文提供了一个行之有效的论文写作框架，并附有涵盖材料、机械系统和电子学的范文及注释。利用这些策略，你可以将零散的想法转变为连贯、对考官友好的答案。
1. Decoding the Essay Prompt | 解码论文题目
Read the question twice, underlining command words such as ‘explain’, ‘discuss’ or ‘evaluate’. For example, ‘Explain how the microstructure of steel affects its mechanical properties’ demands a causal sequence, whereas ‘Evaluate the suitability of aluminium vs. steel for a bicycle frame’ requires balanced comparisons and a justified conclusion. Identify the key engineering concepts involved – is it stress analysis, material science, or energy systems?
把题目读两遍，在“解释”、“讨论”或“评价”等指令词下划线。例如，“解释钢的微观结构如何影响其力学性能”要求给出因果顺序，而“评价铝和钢对自行车车架的适用性”则需要平衡的比较和有理由的结论。确定涉及的关键工程概念——是应力分析、材料科学，还是能量系统？
Circle the context words, such as ‘bicycle frame’, ‘suspension bridge’ or ‘motor controller’. These define the boundaries of your essay. A common mistake is to write generally about a topic without linking back to the specific application given. Plan to refer to the context in every paragraph.
圈出语境词，如“自行车车架”、“悬索桥”或“电机控制器”。它们定义了文章的范围。一个常见错误是泛泛地写一个主题，而不联系题目给出的具体应用。要计划在每一段都提及这个语境。
2. Planning: The 5-Minute Brainstorming Map | 规划：五分钟头脑风暴图
Before writing, spend up to five minutes creating a mind map or a bulleted plan. Start with a central idea – the essay’s main argument. Then branch into three or four core points; each point can become a body paragraph. Under each branch, note specific technical terms, equations and a real-world case. This prevents you from forgetting crucial evidence under time pressure.
动笔前，花最多五分钟制作一个思维导图或要点计划。从一个中心思想——文章的主要论点——开始。然后分出三到四个核心要点，每个要点可以成为一个主体段落。在每个分支下，记下具体的技术术语、方程和一个实际案例。这样可以防止你在时间压力下遗忘关键论据。
For instance, a question on ‘factors affecting the efficiency of a gear train’ might have branches: friction losses, gear tooth profile, lubrication, and bearing quality. Under each, jot down useful symbols like η = Pₒᵤₜ/Pᵢₙ, and data such as typical efficiency ranges for spur vs. helical gears.
例如，一个关于“影响齿轮系效率的因素”的题目可能有如下分支：摩擦损失、齿轮齿形、润滑以及轴承质量。在每个分支下，记下有用的符号如 η = Pₒᵤₜ/Pᵢₙ，以及直齿轮和斜齿轮的典型效率范围等数据。
3. Essay Structure: The 4-Part Blueprint | 论文结构：四部分蓝图
Adopt a consistent four-part structure: a brief introduction, 2–4 body paragraphs, a synthesising conclusion, and a final check. The introduction should define key terms and state the scope: ‘This essay will analyse three microstructural features – grain size, phase distribution and dislocations – and explain how each influences the yield strength of carbon steel.’
采用一个固定的四部分结构：简要引言、2–4 个主体段落、一个综合性的结论以及最后的检查。引言应定义关键术语并说明范围：“本文将分析三个微观结构特征——晶粒尺寸、相分布和位错，并解释每个特征如何影响碳钢的屈服强度。”
Each body paragraph starts with a topic sentence that presents one clear idea. Follow with technical explanation, a calculation or diagram reference, and a link back to the question. Avoid a running commentary; make every sentence earn its place by advancing the argument.
每个主体段落以一个提出明确观点的主题句开头。接着是技术解释、计算或图表引用，再回扣题目。避免流水账；让每一句话都通过推进论点来体现价值。
The conclusion does not simply repeat points but draws them together. For an ‘evaluate’ question, explicitly state which option is better under given conditions and why, mentioning trade-offs. For an ‘explain’ question, summarise the cause–effect chain.
结论不是简单复述要点，而是综合归纳。对于“评价”类问题，要明确指出在给定条件下哪种选择更优及其原因，并提及权衡取舍。对于“解释”类问题，则总结因果链。
4. Embedding Technical Vocabulary Naturally | 自然融入技术词汇
Use precise engineering terminology: instead of ‘stretchiness’, write ‘elastic modulus’ or ‘stiffness’; instead of ‘things that stop movement’, use ‘frictional forces’ or ‘damping’. But avoid ‘keyword stuffing’. The mark scheme rewards accurate application in context, not isolated definitions.
使用精确的工程术语：用“弹性模量”或“刚度”代替“拉伸性”；用“摩擦力”或“阻尼”代替“阻碍运动的东西”。但要避免关键词堆砌。评分标准奖励在语境中的准确应用，而非孤立的定义。
Merge terminology with analysis: ‘The introduction of a carbon-fibre-reinforced polymer (CFRP) skin on the wing increases the specific modulus (E/ρ), allowing a lighter structure without sacrificing stiffness. This is critical because the bending stiffness EI must resist flutter at high speeds.’ Note how terms are explained within the reasoning.
将术语与分析结合：“在机翼上引入碳纤维增强聚合物（CFRP）蒙皮可提高比模量（E/ρ），从而在不牺牲刚度的情况下减轻结构重量。这一点至关重要，因为弯曲刚度 EI 必须抵抗高速时的颤振。”注意术语如何在推理中被解释。
If you introduce a formula, explain every symbol.
σ = F/A
is not enough. You should write: ‘where σ is tensile stress (N/m² or Pa), F is the applied force (N), and A is the original cross-sectional area (m²). Stress concentration at a notch increases local σ, possibly exceeding the yield strength and initiating failure.’
如果引入一个公式，要解释每个符号。
σ = F/A
是不够的。你应该写：“其中 σ 是拉伸应力（N/m² 或 Pa），F 是施加的力（N），A 是原始横截面积（m²）。缺口处的应力集中会增加局部 σ，可能超过屈服强度并引发失效。”
5. Using Diagrams and Equations to Boost Clarity | 利用图表与方程提升清晰度
A well-labelled sketch can replace a lengthy description. Even a simple free-body diagram with forces resolved into horizontal and vertical components clarifies a complex structural problem. Annotate your diagram directly: label tension T, angle θ, and add equations like T sinθ = W/2 beside it. Examiners see that you can model real situations.
一张标注清晰的草图可以代替冗长的描述。即使是一张简单的受力分析图，将力分解到水平和垂直方向，也能清晰说明复杂的结构问题。直接在图上标注：标出拉力 T、角度 θ，并在旁写下方程如 T sinθ = W/2。考官会看到你能够模拟真实情况。
Equations must be logically integrated. Do not just drop a formula. Show progression: ‘From Newton’s second law, F = ma; for the lift system, the net force is motor thrust minus weight, so a = (Fₘ − mg)/m. Substituting m = 800 kg, Fₘ = 9.5 kN gives a = (9500 − 800×9.81)/800 ≈ 2.04 m/s².’ Centre key equations for emphasis but keep explanatory text around them.
方程必须逻辑地整合进去。不要只是扔出一个公式。体现推导过程：“根据牛顿第二定律，F = ma；对于电梯系统，合力等于电机推力减去重力，因此 a = (Fₘ − mg)/m。代入 m = 800 kg，Fₘ = 9.5 kN，得到 a = (9500 − 800×9.81)/800 ≈ 2.04 m/s²。”将关键方程居中加粗来强调，但周围保留解释性文字。
Reference industry standards where relevant: ‘According to the IEC 60034-1 efficiency classes, an IE3 motor at 75% load maintains η > 92%. This informs our selection for the conveyor drive, as operating cost over 10 years dominates the total cost of ownership.’
在相关处引用行业标准：“根据 IEC 60034-1 效率等级，IE3 电机在 75% 负载下保持 η > 92%。这为我们选择输送机驱动装置提供了依据，因为 10 年的运行成本在整个生命周期成本中占主导地位。”
6. Handling Common Command Words | 应对常见指令词
Explain: Give reasons for a phenomenon. Use ‘because’, ‘due to’, ‘as a result of’. For example, ‘The LED driver circuit includes a current-limiting resistor because the forward voltage drop of the LED is nearly constant, and excess voltage would cause a current surge, overheating the junction.’
解释：说明现象的原因。使用“因为”、“由于”、“鉴于”。“LED 驱动电路包含一个限流电阻，因为 LED 的正向压降近乎恒定，多余的电压会引起电流浪涌，使结过热。”
Discuss: Present different aspects, both positive and negative. Use phrases like ‘one advantage is … however, a limitation is …’. ‘Hydraulic actuators provide high force density, but they require regular maintenance of seals and fluid. In contrast, electromechanical actuators offer better controllability but lower power-to-weight ratio.’
讨论：呈现正反两面。用“一个优点是……然而，限制是……”。“液压执行器提供高力密度，但需要定期维护密封件和流体。相比之下，电动机械执行器可控性更好，但功重比较低。”
Evaluate: Make a judgement based on evidence. Weigh criteria like cost, performance, sustainability. Conclude: ‘For an urban car door mechanism where noise and energy efficiency are paramount, an electric actuator is preferable despite higher initial cost, due to lower life-cycle CO₂ emissions and quieter operation.’
评价：基于证据做出判断。权衡成本、性能、可持续性等标准。结论：“对于噪音和能效至关重要的城市汽车车门机构，尽管初始成本较高，电动执行器更可取，因为它整个生命周期的 CO₂ 排放更低且运行更安静。”
Calculate/Determine: Show all steps, substitute values, give units and check the answer’s magnitude. If the required force seems too small or huge, state that you have checked and it is reasonable. This critical thinking impresses examiners.
计算/确定：展示所有步骤，代入数值，给出单位并检查量级。如果计算出的力看起来太小或太大，说明你已经检查过且它是合理的。这种批判性思维会给考官留下深刻印象。
7. Sample Essay 1: Materials Selection for a Cantilever Beam | 范文 1：悬臂梁的材料选择
Prompt: Evaluate the use of mild steel, aluminium alloy 6061-T6, and CFRP for a 2-metre cantilever beam supporting a static load of 5 kN at its free end, considering strength, stiffness, mass and cost.
题目：评价低碳钢、6061-T6 铝合金及碳纤维增强聚合物（CFRP）在一根 2 米长悬臂梁中的使用，自由端承受 5 kN 静载，从强度、刚度、重量和成本角度考虑。
The maximum bending moment Mₘₐₓ at the fixed end is given by M = F × L = 5000 N × 2 m = 10 000 N·m. The required section modulus Z = M/σ_{allow}. Assuming a safety factor of 2, the allowable stress for mild steel (yield strength ~250 MPa) is 125 MPa, so Z = 10 000 / (125 × 10⁶) = 80 × 10⁻⁶ m³ = 80 cm³. A standard I-beam with Z ≈ 100 cm³ would suffice, mass per metre ~20 kg, giving total mass 40 kg. Material cost is low (~£0.80/kg), beam cost ≈ £32.
固定端处最大弯矩 Mₘₐₓ 由 M = F × L = 5000 N × 2 m = 10 000 N·m 给出。所需截面模量 Z = M/σ_{allow}。取安全系数为 2，低碳钢（屈服强度约 250 MPa）的许用应力为 125 MPa，因此 Z = 10 000 / (125 × 10⁶) = 80 × 10⁻⁶ m³ = 80 cm³。一根标准工字钢 Z ≈ 100 cm³ 就足够，每米质量约 20 kg，总重 40 kg。材料成本低（约 £0.80/kg），梁成本约 £32。
For aluminium 6061-T6, yield strength ~276 MPa, allowable 138 MPa, resulting Z = 72.5 cm³. A similar shape can be selected, giving mass ~14 kg/m, total 28 kg. Aluminium’s density (2700 kg/m³) is one-third that of steel, so weight saving is 30%. However, deflection δ = FL³/(3EI) must be checked. Aluminium’s E is 69 GPa vs. steel’s 210 GPa, so deflection triples for the same section. Therefore, a deeper section is needed to match stiffness, partially offsetting mass advantage. Cost is higher (~£2.50/kg), so beam cost ~£70.
对于 6061-T6 铝合金，屈服强度约 276 MPa，许用应力 138 MPa，得出 Z = 72.5 cm³。可选类似截面，质量约 14 kg/m，总重 28 kg。铝的密度（2700 kg/m³）是钢的三分之一，减重 30%。但需校核挠度 δ = FL³/(3EI)。铝的 E 为 69 GPa，而钢为 210 GPa，相同截面下挠度会变为三倍。因此需采用更深的截面来匹配刚度，部分抵消质量优势。成本更高（约 £2.50/kg），梁成本约 £70。
CFRP can be tailored: unidirectional fibres along the beam, giving E up to 130 GPa, density ~1600 kg/m³. Assuming allowable stress 600 MPa, required Z = 16.7 cm³, mass could be below 8 kg. However, cost is ~£30/kg, beam cost ~£240, and connections require bonded or precision-machined inserts, raising fabrication cost. Environmental degradation and impact sensitivity also limit applicability. For a static indoor structure, CFRP offers excessive strength at high cost; aluminium is a good compromise when mass matters, but mild steel remains the most cost-effective solution.
CFRP 可定制：沿梁方向单向纤维，E 可达 130 GPa，密度约 1600 kg/m³。假设许用应力 600 MPa，所需 Z = 16.7 cm³，质量低于 8 kg。然而，成本约 £30/kg，梁成本约 £240，且连接需要粘接或精密机加嵌件，增加了制造成本。环境老化和冲击敏感性也限制了其适用性。对于静态室内结构，CFRP 强度过高且昂贵；当质量重要时，铝是良好折衷，但低碳钢仍是性价比最高的方案。
In conclusion, the choice depends on design priority. If minimum cost and simplicity are vital, mild steel wins. If weight saving is crucial (e.g. aerospace feeder structure), aluminium 6061-T6 offers a balance. CFRP is only justified when extreme weight reduction trumps all other factors.
总之，选择取决于设计优先级。若最低成本和简单性至关重要，低碳钢胜出。若减重很关键（如航空供料结构），6061-T6 铝合金提供了一个平衡。CFRP 仅在极端减重需求压倒其他所有因素时才是合理的。
8. Sample Essay 2: Efficiency of a Compound Gear Train | 范文 2：复合齿轮系的效率
Explain the factors that influence the overall efficiency of a two-stage compound gear train and suggest how each can be optimised.
解释影响两级复合齿轮系整体效率的因素，并说明如何优化每个因素。
Overall efficiency η = η₁ × η₂, where η₁ and η₂ are efficiencies of each stage. The dominant factor is friction between meshing teeth. This friction depends on the sliding velocity, which is proportional to the gear ratio and speed. In a high-ratio stage, sliding losses increase, so efficiency typically drops. Using helical gears instead of spur gears increases contact ratio, reducing sliding per tooth and raising η to 98% per stage versus 95% for spur. However, helical gears generate axial thrust, requiring thrust bearings that introduce additional losses.
总效率 η = η₁ × η₂，其中 η₁ 和 η₂ 是每级的效率。主导因素是啮合齿间的摩擦。该摩擦力取决于滑动速度，而滑动速度与传动比和转速成正比。在高传动比级，滑动损失增大，因此效率通常会下降。使用斜齿轮代替直齿轮可提高重合度，降低每齿的滑动量，将每级效率提升至 98%（直齿轮为 95%）。但斜齿轮产生轴向推力，需要推力轴承，从而引入额外损失。
Lubrication is critical. Full-film elastohydrodynamic lubrication separates tooth surfaces, cutting friction coefficient from ~0.1 (boundary) to ~0.02. Selecting synthetic oils with appropriate viscosity at operating temperature maintains film thickness. Regular oil analysis prevents efficiency decay from contamination.
润滑至关重要。全膜弹流润滑将齿面隔开，摩擦系数从约 0.1（边界润滑）降至约 0.02。选用在工作温度下具有合适粘度的合成油可维持油膜厚度。定期油液分析可防止因污染导致的效率下降。
Bearing losses: deep-groove ball bearings have lower friction than plain bearings. Preloading can improve stiffness but increases friction torque. Optimising bearing selection and preload can recover 1–2% overall efficiency.
轴承损失：深沟球轴承的摩擦力低于滑动轴承。预紧可以提高刚度，但会增加摩擦力矩。优化轴承选型和预紧力可回收 1–2% 的整体效率。
Finally, gear geometry: precision-ground tooth profiles reduce transmission error and vibration, which otherwise dissipate energy. Applying surface coatings like diamond-like carbon (DLC) reduces boundary friction during start-stop. Combining these, a two-stage compound gear train can achieve η > 96%, compared to ~85% in a poorly designed setup.
最后是齿轮几何形状：精密磨削的齿形可降低传动误差与振动，否则这些会耗散能量。应用类金刚石（DLC）表面涂层可减少启停时的边界摩擦。结合这些措施，一个两级复合齿轮系可实现 η > 96%，而设计不佳的装置可能只有约 85%。
9. Sample Essay 3: Transistor as a Switch in a Motor Control Circuit | 范文 3：三极管在电机控制电路中的开关应用
Discuss the use of a MOSFET as a low-side switch to drive a 12 V DC motor, including protection features and efficiency considerations.
讨论使用 MOSFET 作为低边开关驱动 12 V 直流电机，包括保护功能和效率考虑。
An N-channel MOSFET, such as the IRLZ44N, is placed between the motor’s negative terminal and ground. When gate-source voltage V_GS exceeds the threshold (typically 2–4 V), the MOSFET turns on, presenting a very low drain-source resistance R_DS(on) of about 0.022 Ω. At a motor current of 5 A, the voltage drop V_DS = 5 × 0.022 = 0.11 V, so power dissipation as heat in the MOSFET is P = I²R = 5² × 0.022 = 0.55 W. This is far lower than a bipolar junction transistor, where V_CE(sat) might be 0.7 V, leading to 3.5 W. Hence, MOSFETs are more efficient.
一个 N 沟道 MOSFET，如 IRLZ44N，置于电机负端与地之间。当栅源电压 V_GS 超过阈值（通常 2–4 V）时，MOSFET 导通，呈现出极低的漏源电阻 R_DS(on) 约 0.022 Ω。在 5 A 电机电流下，压降 V_DS = 5 × 0.022 = 0.11 V，MOSFET 的发热耗散功率为 P = I²R = 5² × 0.022 = 0.55 W。这远低于双极结型三极管，后者的饱和压降 V_CE(sat) 可能为 0.7 V，导致 3.5 W。因此 MOSFET 效率更高。
A flyback diode must be connected anti-parallel to the motor to clamp the inductive voltage spike when the MOSFET turns off. Without it, the energy stored in the motor inductance (½LI²) could generate a high voltage that exceeds the MOSFET’s drain-source breakdown voltage V_DSS, destroying it. A Schottky diode like 1N5819 is preferred for its low forward voltage and fast recovery.
必须在电机两端反并联一个续流二极管，以在 MOSFET 关断时钳位电感的电压尖峰。否则，储存在电机电感中的能量（½LI²）可能产生高压，超过 MOSFET 的漏源击穿电压 V_DSS，将其损坏。肖特基二极管如 1N5819 因其低正向压降和快恢复时间而更受青睐。
Gate drive: a microcontroller pin cannot supply the transient gate current needed for fast switching. A gate driver or a simple push-pull transistor buffer ensures rapid charging of gate capacitance, minimising time in the linear region where R_DS is intermediate and power loss soars. Efficiency also demands using PWM (Pulse Width Modulation) for speed control, keeping the MOSFET in fully on or fully off states as much as possible.
栅极驱动：微控制器引脚无法提供快速开关所需的瞬态栅极电流。一个栅极驱动器或简单的推挽三极管缓冲电路可确保栅极电容快速充电，最小化在线性区的时间，此期间 R_DS 为中间值，功率损耗猛增。效率还要求使用 PWM（脉冲宽度调制）进行调速，尽可能使 MOSFET 处于完全导通或完全关断状态。
Protection: include a gate-source zener diode to clamp voltage to safe limits (<20 V). A small series gate resistor damps oscillations. With these measures, the MOSFET switch can handle 5 A continuously with minimal heatsinking, demonstrating a robust, efficient solution for small electric vehicle actuators.
保护：加入一个栅源齐纳二极管，将电压钳位在安全限值内（<20 V）。一个小的串联栅极电阻可阻尼振荡。采取这些措施，MOSFET 开关可在极小散热需求下连续处理 5 A 电流，为小型电动车执行器提供了一个稳健、高效的方案。
10. Adapting the Framework to Different Topics | 将框架适应不同主题
The four-part structure works universally. For a ‘mechanics and structures’ essay, body paragraphs might cover free-body analysis, stress calculations, material limits and design codes. For ‘electronics’, they can address component choice, circuit analysis, signal processing and compliance with standards. The key is always linking engineering science back to the application mentioned in the question.
四部分结构是通用的。对于“力学与结构”论文，主体段落可能涵盖受力分析、应力计算、材料极限和设计规范。对于“电子学”，可涉及元件选择、电路分析、信号处理和符合标准。关键始终是将工程科学链接回题目中提到的应用。
Even within a topic, you can vary the angle. A question on ‘comfort in a car suspension’ might blend human vibration perception (ISO 2631) with damping coefficient calculations. Show the examiner you can connect hard numbers to human factors. Use phrases like ‘The damping ratio ζ = 0.3–0.5 is optimal for ride comfort, balancing overshoot and settling time.’
即使在同一个主题内，你也可以变换角度。一个关于“汽车悬架舒适性”的问题，可以将人体振动感知（ISO 2631）与阻尼系数计算相结合。向考官展示你能把硬核数据与人为因素联系起来。使用诸如“阻尼比 ζ = 0.3–0.5 对乘坐舒适性最优，平衡了超调量和稳定时间”的表达。
11. Time Management: Allocating the 30 Minutes | 时间管理：分配 30 分钟
A typical extended essay question carries 8–12 marks and should take about 25–30 minutes. Use the following split: 5 minutes planning, 20 minutes writing, 5 minutes reviewing. Stick to this ruthlessly; a perfect plan with little writing scores less than a moderate essay with a clear thread.
一个典型的论文题目占 8–12 分，约需 25–30 分钟。使用如下划分：5 分钟规划，20 分钟写作，5 分钟回顾。严格坚持；一个完美计划但写得很少的答案，得分会低于一篇条理清晰的中等文章。
During the review, verify that every equation is dimensionally consistent (e.g., N/m² is indeed Pa). Check that you have directly answered the command word – have you ‘evaluated’ by making a judgement, or just ‘explained’? Tidy up diagrams, add missing units, and correct any spelling errors in technical terms.
在回顾阶段，验证每个方程量纲一致（例如 N/m² 确实是 Pa）。检查你是否直接回应了指令词——你是否通过做出判断来“评价”了，还是仅仅“解释”了？整理图表，添加遗漏的单位，纠正技术术语中的拼写错误。
12. Examiner Tips and Final Advice | 考官建议与最后忠告
Examiners report that essays scoring top marks always demonstrate ‘clear logical progression’ and ‘specific application to context’. Generic answers rarely move beyond the mid-level. Use the PEEL technique: Point, Evidence (calculation/data), Explanation (why it works), Link (back to question).
考官报告显示，获得高分的论文总是“逻辑推进清晰”且“对语境有具体应用”。泛泛而谈的答案很少超出中间档。使用 PEEL 手法：观点、证据（计算/数据）、解释（为什么有效）、联系（回扣题目）。
Avoid the ‘silo’ approach where you write a paragraph about stress, another about materials, with no connections. Blend concepts: ‘The lower Young’s modulus of aluminium increases deflection, so a deeper section is needed – this ties stiffness directly to material property.’ Interweaving concepts signals a higher-order understanding.
避免“孤岛”写法，即一段写应力，另一段写材料，彼此无联系。要融合概念：“铝较低的杨氏模量增大了挠度，因此需要更深的截面——这把刚度和材料属性直接关联起来。”交织概念标志着更高层次的理解。
Finally, practice writing essays under timed conditions using past papers. Then compare your response with the mark scheme and sample answers published by Edexcel. Identify gaps in your technical depth and refine your framework. With consistent practice, the essay section becomes the most reliable source of high marks.
最后，用过去的试卷在限时条件下练习论文写作。然后将你的回答与 Edexcel 发布的评分方案和范例答案进行比较。找出技术深度上的差距并完善你的框架。通过持续练习，论文部分将成为最可靠的高分来源。
Published by TutorHao | Engineering Revision Series | aleveler.com
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