2025年12月英语四级第1套真题句子解析： This cycle is the reason why people rest at night and are active during the day.

This cycle is the reason why... (名词性表达与原因说明)

This cycle is the reason why

"the reason why..." 是英语中表达因果关系的标准结构,其中 "why" 引导说明原因的内容。需要注意的是,"reason" 后既可接 "why",也可接 "that",两者在现代英语中都可接受,但 "why" 更常用且更符合逻辑(reason 本身含 "为什么" 之意)。本句中 "This cycle" 是主语,"is" 是系动词,"the reason" 是表语,整体构成 "A is the reason why B" 模式,表达 "A 是 B 的原因"。这种结构在学术写作和说明性文本中极为常见,用于建立明确的因果关系链。

• ✓ This is the reason why we need to act now. ✗ This is the reason that why we need to act now. / This is why reason we need to act now. 不要在 "reason why" 中间插入 "that",也不要颠倒 "reason" 和 "why" 的顺序。
• ✓ The reason (why/that) he left is unclear. ✗ The reason because he left is unclear. "reason" 后不接 "because",因为 "reason" 本身已含原因之意,两者语义重复。

rest at night and are active during the day (平行结构与时间对比)

rest at night are active during the day

本句使用 "rest at night" 和 "are active during the day" 构成平行结构,通过 "and" 连接两个并列的动词短语,形成鲜明对比。需注意的语法细节:两个动词短语共用主语 "people",第二个动词短语保留了 "are" 而省略了主语,这是英语中避免重复的标准做法。时间状语 "at night" 与 "during the day" 的选用也值得关注:"at night" 用 "at" 表示特定时间点的概念,"during the day" 用 "during" 强调持续的时间段。这种 "at night" vs "during the day" 的搭配是固定用法,体现了英语中时间介词的微妙差异。平行结构不仅使句子对称工整,也强化了昼夜节律的对立性。

• ✓ People rest at night and are active during the day. ✗ People rest at night and active during the day. 平行结构中,第二个动词短语省略主语但不能省略助动词/系动词 "are",否则结构不完整。
• ✓ at night / during the day ✗ in the night / at the day "at night" 和 "during the day" 是固定搭配,不可随意替换介词。"at night" 强调时间点,"during the day" 强调时间段。

cycle (生物学术语的日常化使用)

cycle

"cycle" 在本句中指生物钟或昼夜节律周期(circadian rhythm),是一个从科学术语向日常表达过渡的词汇。在学术语境中,"cycle" 指任何重复发生的过程或现象,如 "life cycle"(生命周期)、"economic cycle"(经济周期)。本句语境下特指生理性的周期性规律。"cycle" 作为可数名词,强调完整的循环过程,从起点回到起点的闭环特征。这个词在四六级和考研中常以 "a cycle of..."、"the cycle of..." 形式出现,也常见动词用法 "cycle through"(循环经历)。中文学习者需要理解 "cycle" 不仅指自行车,在学术和正式语境中更多表示周期、循环的抽象概念。

• ✓ the water cycle / a cycle of growth and decline ✗ the water circle / a circle of growth and decline 表示周期性循环用 "cycle" 而非 "circle"。"circle" 指圆形或圈子,"cycle" 指时间或过程上的周期循环。

rest (动词的基础但多义用法)

rest

"rest" 在本句中作不及物动词,表示 "休息、静止"。虽然是基础词汇,但 "rest" 的用法比初学者想象的更丰富:作动词时可表示 "休息"(rest for a while)、"倚靠"(rest against the wall)、"基于"(rest on evidence);作名词时表示 "休息"(take a rest)、"剩余部分"(the rest of...)。本句中 "rest at night" 构成动词+时间状语的简单搭配,表达人在夜晚处于休息状态。需要注意 "rest" 与 "sleep" 的区别:"rest" 侧重停止活动、放松恢复,不一定睡觉;"sleep" 明确指睡眠。本句用 "rest" 而非 "sleep",涵盖了包括睡眠在内的所有夜间低活动状态。

• ✓ I need to rest. / Let's take a rest. ✗ I need to take rest. (在某些语境下不自然) "rest" 作动词时直接用 "rest",不必加 "take";作名词时才说 "take a rest"。两种用法都对,但要区分词性。

be active (系表结构表示状态)

are active

"be active" 是系动词+形容词构成的系表结构,表示 "处于活跃状态"。"active" 作形容词,表示 "活跃的、积极的、主动的",反义词是 "passive"(被动的)或 "inactive"(不活跃的)。在生理或行为语境中,"be active" 指从事各种活动、精力充沛、身体活动多;在语态或语法语境中,"active" 指主动语态。本句中 "are active during the day" 与 "rest at night" 形成对比,通过系表结构简洁地描述人类的昼夜活动模式。"be active" 可与多种介词和状语搭配,如 "be active in..."(在某方面活跃)、"be active at..."(在某时活跃)。

• ✓ She is active in community service. / They are active during summer. ✗ She is very activity. / They are activeness. "active" 是形容词,不要误用名词形式 "activity"(活动)或 "activeness"(活跃性)。

at night vs during the day (时间介词的精准选择)

at night during the day

英语中时间介词的选用极为讲究,"at night" 与 "during the day" 的搭配体现了这一点。"at" 通常用于具体时刻(at 3 o'clock)或被视为时间点的时段(at night, at noon, at midnight),强调时间的点状特征;"during" 用于较长的时间段(during the week, during summer),强调在某段时间的延续过程中。"night" 虽然是一段时间,但英语习惯上用 "at night" 将其视为一个整体时间点;而 "day" 作为白天时段,常用 "during the day" 强调持续性。这种用法是约定俗成的,初学者容易混淆。另外,"in the night" 也存在但更强调夜晚内部的某个时刻(如 "in the dead of night"),而 "at night" 是更通用的 "在夜间" 表达。

• ✓ at night, at noon, at midnight / during the day, during the morning ✗ in the night (作为通用表达), at the day 表示 "在夜间" 的常规说法是 "at night",不说 "at the night" 或 "in the night"(后者仅在特定文学或强调语境使用);"在白天" 说 "during the day" 或 "in the daytime",不说 "at the day"。
• ✓ I work during the night shift. ✗ I work at the night shift. 当 "night" 搭配具体的时间段概念(如 "night shift" 夜班),可用 "during";但单独说 "在夜里" 仍用 "at night"。

科普说明性句式的典型特征

This cycle is the reason why people rest at night and are active during the day.

本句是典型的科普说明句式,具有以下特征:1) 使用指示代词 "This" 承上启下,指代前文提到的某个概念(此处为昼夜节律);2) 采用 "A is the reason why B" 结构明确建立因果关系,逻辑清晰;3) 使用简单现在时(is, rest, are)陈述客观规律;4) 通过对比性并列结构(rest vs active, night vs day)增强说服力和可读性。这种句式在学术文章的解释段落、科普读物、考试阅读理解中极为常见,是中文学习者需要熟练掌握的说明性表达模式。句子长度适中(17词),结构清晰,既不过分简单也不冗长复杂,适合用于承接前文并引出解释。