七、定语从句和状语从句(Attributive Clauses and Adverbial Clauses)
　　定语从句
　　定语从句也称为关系从句或形容词性从句，由关系代词who, whom, whose, which, that或关系副词as, when, where, why等引导。关系词除了起引导作用外，还在从句中指代前面的先行词，并在从句中担任一定的成分。如：
　　The car which was stolen has been found.(which指代先行词car，在从句中作主语)
　　The house whose windows are broken is empty.(whose是所有格，在从句中作定语)
　　I shall never forget the day when I entered the university.(when指代先行词day，在从句中作时间状语)
　　1. 限定性定语从句和非限定性定语从句
　　定语从句就其与先行词的关系而言，可分为限定性定语从句和非限定性定语从句。限定性定语从句和先行词之间没有逗号，表示对先行词起修饰限制作用;而非限定性定语从句和先行词之间有逗号分开，是对先行词进行补充说明，相当于并列句。如：
　　He is the man who has strong personality. (限定性定语从句)
　　My mother, who works abroad, is coming next week. (非限定性定语从句)
　　注：1)非限定性定语从句不能用that引导，一般用which, as或who(指人)。用which或as引导时，既可以修饰主句的部分内容，也可修饰主句的全部内容。如：
　　He spoke confidently, which impressed me most. (which指代整个主句，在从句中作主语)
　　2)as引导的非限定性定语从句既可放在主句之前，也可以放在主句之后，但which或who引导的非限定性定语从句不能放在主句之前。如：
　　As we all know, the moon is a satellite of the earth.
　　The large area is covered with thick snow, which affects people’s life greatly.
　　3) 在限定性定语从句中，关系代词作宾语时可以省略;但在非限定性定语从句中，关系代词作宾语时不能省略。如：
　　The film (which) I saw last night is about a young teacher. (which可以省去)
　　She introduced me to her husband, whom I hadn’t met before. (whom不能省去)
　　2. 通常只用关系代词that，不用which, who或whom的几种情况
　　1)当先行词是all, everything, nothing, something, anything, little, much, none, few等时，如：
　　All that you want is here.
　　2) 当先行词被all, no, some, any, every, a few, a little, much, only, very等修饰时。如：
　　There is no person that doesn’t make mistakes.
　　3) 当先行词被序数词或形容词最高级修饰时。如：
　　This is the best film that I have ever seen.
　　4) 当出现两个或两个以上的先行词，并同时兼指人或物时。如：
　　We are talking about the people and countries that we have visited.
　　5) 当主句是以which或who开头的特殊疑问句时。如：
　　Who is the person that is standing over there?
　　6) 当定语从句为there be句型时，关系代词只能用that，但经常可以省略。如：
　　I know the difference (that) there is between you.
　　7) 当关系代词在从句中作表语时，常用that。如：
　　He does not seem to be the man that he was. 他似乎和过去不一样了。
　　3. 与其他词连用引导的定语从句
　　As引导定语从句时，可指人也可指物，通常与the same, such, so等连用，形式为：the same … as, such … as, as … as, so … as。as在定语从句中可作主语、宾语、表语等。如：
　　She knew he felt just the same as she did. 她知道他的感觉与她自己的一样。(as代替事，作宾语)
　　I lend you such books as will interest you. 我借给你使你感兴趣的书。(as代替物，作主语)
　　注：the same … as和the same … that的用法不同。as引导的定语从句表示其内容与主句所讲的事物“相似”，指同类事物;that引导的定语从句表示其内容与主句所讲的事物是“同一个”，指同一事物。如：
　　This is the same pen as I lost yesterday. 这和我昨天丢的笔一样。(类似的笔)
　　This is the same pen that I lost yesterday. 这支笔就是我昨天丢的那支。(同一支笔)
　　4. “介词 + 关系代词”引导的定语从句
　　在“介词 + which / whom”结构中，介词的选择取决于三种情况：
　　1)定语从句中谓语动词与表语的搭配。如：
　　This is the college in which I am studying.
　　He is the man about whom we are talking.
　　2) 先行词与介词的习惯搭配。如：
　　The speed at which the machine operates is known on the meter.
　　3)当定语从句为最高级时只能用of which;否则用其他介词。如：
　　I have five dictionaries of which Longman Dictionary is the best.
　　I have five dictionaries among which Longman Dictionary is published in UK.
　　注：不可拆分的动词短语介词不能提前，如put up with;有的短语可能有不同的介词搭配，此时需要根据上下文来确定。如：be familiar with / to, compare with / to等。
　　有时为表意清楚，还可以在关系副词where / when前加介词from, to等。如：
　　China is the birthplace of kites, from where kite flying spread to Japan, Thailand and India.