复数与介词：每篇作文都会重复出现的错误

In Mandarin, 三本书 uses the same noun 书 as 一本书 — quantity is carried entirely by the number and measure word, and the noun itself never changes. English instead requires the noun to change ("three books") independent of whether a number is even present: "many students", "few resources", "most countries" all need the plural noun even though no digit appears. Under time pressure, Chinese speakers reliably drop the -s specifically in two places: after quantity words other than a literal number (many, several, various, a range of), and on nouns separated from their quantity word by other words ("the three most important factor" — the adjective "important" sits between "three" and the noun, making it easy to forget the noun needs marking too). The fix during proofreading is mechanical: find every plural quantity word and trace forward to its noun, no matter how many words sit between them.

在中文里，"三本书"和"一本书"用的是同一个名词"书"——数量完全由数词和量词承担，名词本身从不改变。英语则要求名词本身变化（"three books"），而且这种变化与句子里是否出现具体数字无关："many students"、"few resources"、"most countries" 这些说法即使没有出现具体数字，名词也必须用复数。在时间压力下，中文母语者最常在两个地方漏掉 -s：一是跟在"many、several、various、a range of"这类非具体数字的数量词后面；二是名词与数量词之间被其他词隔开的时候（比如 "the three most important factor"——形容词 "important" 插在 "three" 和名词之间，很容易让人忘记名词也需要加复数标记）。校对时的解决方法很机械：找出每一个表示复数概念的数量词，一路向后追踪到它所修饰的名词，无论中间隔了多少个词。

Prepositions cause more errors than almost any other word class because Mandarin coverbs (在, 于, 关于, 依赖) do not map one-to-one onto English prepositions — the mapping has to be memorized case by case, not translated. Four patterns cover a large share of exam errors. Time: use "in" for months/years/decades ("in July", "in 2020"), "on" for days and dates ("on Monday", "on July 3rd"), "at" for clock times and a few fixed points ("at 9 a.m.", "at night"). Place follows the same logic: "in" for enclosed areas or large regions ("in Taipei", "in the room"), "on" for surfaces ("on the table", "on page 12"), "at" for specific points ("at the entrance", "at the corner"). Two verbs are worth memorizing as exceptions because they take no preposition at all where a direct Mandarin translation would suggest one: "discuss" (not "discuss about") and "attend" (not "attend to" when it means "go to" an event). And "depend on" is the fixed pairing — never "depend to" or "depend for".

介词是造成错误最多的词类之一，因为中文的介词/动词（在、于、关于、依赖）与英语介词并非一一对应——这个对应关系必须逐个记忆，而不能靠直译。有四类模式覆盖了考试中相当大一部分介词错误。时间：月份、年份、年代用 "in"（"in July"、"in 2020"）；具体的日子和日期用 "on"（"on Monday"、"on July 3rd"）；钟点时刻和少数固定说法用 "at"（"at 9 a.m."、"at night"）。地点遵循同样的逻辑：封闭区域或较大范围用 "in"（"in Taipei"、"in the room"）；平面表面用 "on"（"on the table"、"on page 12"）；具体的点用 "at"（"at the entrance"、"at the corner"）。有两个动词值得当作例外单独记住，因为直译成中文会让人以为需要介词，但英语里它们后面完全不加介词："discuss"（不是 "discuss about"）和表示"去参加"某活动时的 "attend"（不是 "attend to"）。而 "depend on" 是固定搭配——绝不能说成 "depend to" 或 "depend for"。