一、核心概念：什么是关系代词？
关系代词，用来引导定语从句，同时代替主句中的某个名词或代词（即先行词），并在从句中充当一定的句子成分。当关系代词在定语从句中作宾语时，它指代先行词，并在从句中承受动作。
关键点： 关系代词作宾语时，可以省略（特别是在口语和非正式文体中）。
二、作宾语的关系代词有哪些？
主要有：whom, which, that, who（口语中who可代替whom）。它们的选择取决于先行词是人还是物。
| 关系代词 | 指代对象 | 正式程度 | 例句（作宾语） |
|---|---|---|---|
| whom | 人 | 正式 | The lady whom we met yesterday is a famous writer. |
| which | 物/动物 | 通用 | The book which I borrowed is very interesting. |
| that | 人/物 | 通用 | This is the best movie that I have ever seen. |
| who (代替whom) | 人 | 非正式 | The friend who I called is coming soon. |
三、深度分析与使用场景
1. 正式 vs. 非正式：whom 与 who/wthat 的选择
在正式写作和考试中，指人作宾语时，应使用 whom。但在日常口语和非正式文体中，常用 who 或 that 代替，甚至直接省略。
| 正式场合 (使用whom) | 非正式场合 (使用who/that/省略) |
|---|---|
| To whom did you send the invitation? | Who did you send the invitation to? / (Who) you sent the invitation to? |
| She is the candidate for whom we voted. | She is the candidate (who/that) we voted for. |
2. which 与 that 指物时的区别
一般情况下，指物时 which 和 that 可以互换。但在非限制性定语从句（用逗号隔开，对先行词进行补充说明）中，必须使用 which，而不能使用 that。
例： His new car, which he bought last week, was stolen. (非限制性定语从句，不能用that)
例： The car that/which he bought last week was stolen. (限制性定语从句，that/which均可)
3. 必须使用 that 的情况
在以下特定情况下，即使作宾语，也优先使用 that，或者只能用 that：
- 先行词是不定代词（all, much, anything, everything, nothing, little, none等）时。
例：Is there anything (that) I can do for you?
- 先行词被序数词、最高级或 the only, the very 等修饰时。
例：This is the best novel (that) I have read this year.
- 先行词同时包含人和物时。
例：We talked about the persons and things (that) we remembered.
四、综合实例演练
通过大量例句来巩固理解（括号内为可省略的关系代词）：
| 句子类型 | 例句（带关系代词） | 例句（省略关系代词） |
|---|---|---|
| 指人 | The student (whom/who/that) the teacher praised is my brother. | The student the teacher praised is my brother. |
| 指物 | The project (which/that) we finished was a success. | The project we finished was a success. |
| 介词前置（正式） | This is the house in which I grew up. | (不可省略) |
| 介词后置（非正式） | This is the house (which/that) I grew up in. | This is the house I grew up in. |
五、常见错误避免
错误1： 在关系代词作宾语时，画蛇添足地添加人称代词。
错误例句： The movie which I saw it yesterday was great. (❌ 多余的it)
正确： The movie (which) I saw yesterday was great. (✅)
错误2： 混淆 who 和 whom 在正式文体中的用法。
错误例句： The man who I work with is from Canada. (非正式可以，正式文体中欠妥)
正式正确： The man with whom I work is from Canada. 或 The man whom I work with is from Canada. (✅)