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定语从句是中学语法中相当重要的一个部分，也是英语考试的常见考点之一。同学们在复习和运用定语从句时应注意以下几个方面：
一、as和which的选择
1. as和which都可以引导非限制性定语从句，用来指代整个主句的内容。非限制性定语从句位于句末且as或which在从句中作主语、宾语或表语时，两者常可互换。如：
He failed in the exam, which / as was natural.
He is an honest boy, which / as anyone can see.
2. 如果非限制性定语从句位于主句之前或插在主句之中时，只能用as。如：
As is known to all, the 2008 Olympic Games are to be held in
3. as在从句中作主语，后面常跟行为动词的被动式；which在从句中作主语，后常跟行为动词的主动式。如：
She has been late again, as was expected.
It rained hard yesterday, which kept me from going to the park.
二、关系代词和关系副词的选择
在英语中，当先行词是地点名词、时间名词或原因名词时，是用关系代词还是关系副词引导定语从句，取决于引导词在定语从句中所充当的成分。若作状语，用关系副词(when, where, why)或介词 + 关系代词(which)；若作主语、宾语或表语，用关系代词(that / which)。如：
This is the place which I visited last year.
（which作visit的宾语）
This is the place where I lived last year.
（where作地点状语）
I’ll never forget the day when I joined the army. （when作时间状语）
I’ll never forget the days which we spent together. （which作spend的宾语）
三、关系代词和人称代词、指示代词的选择
选关系代词还是人称代词或指示代词，关键得分析清句子结构。如果是非限制性定语从句（两句中间以逗号隔开，且无连词），用关系代词；如果是并列句（全句中有连词或两句中间为分号），用人称代词或指示代词。试体会：
He has three sons, none of whom is a writer.
He has three sons, who are writers.
He has three sons, but none of them is a writer.
He has three sons; they are writers.
四、定语从句中数和性的选择
关系代词在定语从句中作主语时，谓语动词要和先行词的性、数保持一致。如：
[误] This is one of the rooms that is free now.
[正] This is one of the rooms that are free now.
[析] 当定语从句先行词是one of ... 结构时，先行词为of后的复数名词或代词，从句谓语动词用复数形式。
[误] He is the only one of the experts who know a little French.
[正] He is the only one of the experts who knows a little French.
[析] 当定语从句先行词是the (only / very) one of ... 结构时，先行词为one，从句谓语动词用单数形式。
五、避免关系词与被替换词重复
定语从句中不能再重复被关系代词或关系副词所替代的部分。
[误] This is the coat which I bought it last month.
[正] This is the coat which I bought last month.
[析] which引导定语从句，又在定语从句中作bought的宾语，再加it就多余了。
[小试] 从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
1. John said he’d been working in the office for an hour, _____ was true. (北京2001春)
A． he B． this C． which D． who
2. Is this the reason _____ at the meeting for his carelessness in his work? (上海2002春)
A. he explained B. what he explained
C. how he explained D. why he explained
3. _____ has been announced, we shall have our final exams next month. (上海2003春)
A. That B. As C. It D. What
4. We are living in an age _____ many things are done on computer. (北京2003春)
A. which B. that C. whose D. when
5. There are two buildings, _____ stands nearly a hundred feet high. (湖北 2004)
A. the larger B. the larger of them
C. the larger one that D. the larger of which
6. Do you still remember the chicken farm _____ we visited three months ago? (北京2005春)
A. where B. when C. that D. what
7. I have many friends, _____ some are businessmen. (2005全国卷Ⅰ)
A. of them B. from which
C. who of D. of whom
8. Mark was a student at this university from 1999 to 2003, _____ he studied very hard and was made Chairman of the Students’ Union. (重庆2005)
A. during which time B. for which time
C. during whose time D. by that time
江西 廖添发 上海 王 鸽
Key: 1-4 CABD 5-8 DCDA
