一、 核心概念
定语从句，又称形容词性从句，是一个用来修饰名词或代词（即先行词）的句子。它通常紧跟在先行词之后，像一个“大尾巴”一样，为这个名词或代词提供更多信息。
二、 解题“三步法”（应对中考关键思路）
1. 找先行词：在主句中找出被修饰的那个词（人或物）。
2. 判成分：分析先行词在后面的定语从句中充当什么角色（主语、宾语还是状语）。
3. 选词填空：根据先行词的意义及其在从句中的成分，选择正确的关系词（that, which, who, whom, whose, when, where, why）。
三、关系词详解
关系代词
· who/that：指人，在从句中作主语或宾语（作宾语时可省略）。
The boy who/that is playing basketball is my classmate. (作主语)
> The lady (who/that) you saw is our principal. (作宾语，可省略)
· whom：指人，在从句中作宾语（可被who或that替代，常省略）。
He is the person (whom) I trust most.
· which/that：指物或动物，在从句中作主语或宾语（作宾语时可省略）。
Here is the book which/that tells the story. (作主语)
> Is this the pen (which/that) you are looking for? (作宾语，可省略)
· whose：指人或物，在从句中作定语，表示“…的”。
Do you know the girl whose father is a doctor? (修饰“father”)
> They live in a house whose roof is red. (修饰“roof” = the roof of which)
关系副词
· when：先行词是时间名词（如time, day, year），在从句中作时间状语。
I’ll never forget the day when (=on which) we graduated.
· where：先行词是地点名词（如place, school, city），在从句中作地点状语。
This is the factory where (=in which) my father works.
· why：先行词只有reason，在从句中作原因状语。
Please tell me the reason why (=for which) you were late.
四、 必考特殊规则与易错点
1. 必须使用 that 的四种情况（中考高频考点）：
· 先行词是不定代词时（如all, everything, nothing, anything）。
中考真题 (2022 武汉)：Is there anything ____ I can do for you?
> A. who B. which C. that D. whom
> 解析：C。先行词为不定代词anything，关系词应用that。
· 先行词被序数词或形容词最高级修饰时。
中考真题 (2021 成都)：This is the best movie ____ I have ever seen.
> A. who B. which C. that D. when
> 解析：C。先行词movie被最高级the best修饰，关系词应用that。
· 先行词被the only, the very, the last等修饰时。
He is the only person that can solve this problem.
· 先行词同时包含人和物时。
We talked about the people and places that impressed us most.
2. 关系词的省略：
· 关系代词（that, which, whom）在从句中作宾语时，通常可以省略。
The music (that) we listened to was relaxing.
· 重要提醒：关系词在从句中作主语时，绝对不能省略。
3. 区分关系代词与关系副词（经典陷阱）：
· 关键看从句缺不缺主语或宾语。缺主/宾，用代词；只缺状语，用副词。
中考真题 (2023 南京)：I still remember the village ____ we visited last summer.
> A. where B. who C. which D. when
> 解析：C。先行词village。判断从句成分：we visited ____ last summer. “参观” village，village在从句中作宾语（参观村庄），因此应选用关系代词which或that（此处作宾语可省略）。如果从句是 “we lived in the village last summer”，则village作地点状语，就应选where。
4. “介词 + 关系代词”结构：此时关系词只能用which(指物)或whom(指人)。
This is the camera with which I took the photos. (= that I took the photos with)
五、 中考真题综合演练
1. (2023 北京) — Do you know the girl ____ is standing under the tree?
— Of course. She is Lucy, my classmate.
A. who B. whom C. which D. whose
解析：A。先行词the girl（人），在定语从句中作主语，故选who。
2. (2022 上海) The reason ____ he gave for his absence was unbelievable.
A. why B. when C. which D. where
解析：C。此题易错选why。分析从句成分：he gave ____ for his absence. “他给出了理由”，“理由”在从句中作gave的宾语，因此应用关系代词which或that（此处作宾语可省略）。如果从句是 “he was absent for the reason”，则reason作原因状语，才选why。
3. (2021 广州) The house ____ we stayed in during the holiday is by the sea.
A. what B. whose C. where D. which
解析：D。先行词the house。从句为：we stayed in ____ during the holiday. “住在房子里”，house在从句中作介词in的宾语，因此用关系代词which或that。where是关系副词，在从句中只能作状语，不能作宾语。
六、 备考总结
· 核心口诀：先看先行词，再看从句缺什么。缺主/宾用that/which/who，缺状用when/where/why。
· 高分关键：务必分析从句本身的结构，判断先行词在从句中的成分，这是避免落入出题陷阱的唯一方法。
· 最后检查：关系词在从句中充当主语或宾语时，从句本身不能再出现重复的主语或宾语。
