定語從句
　　限制和非限制性定語從句: 限制性定語從句是名詞詞組不可缺少的一個組成部分, 去掉了會造成病句或意義不明確; 非限制性定語從句屬于補充說明性質, 去掉了不會影響主要意義, 通常用逗號與它的先行詞分開.
　　The boys who wanted to play football were disappointed when it rained.
　　The boys, who wanted to play football, were disappointed when it rained.
　　如果定語從句的先行詞是專有名詞, 或是帶有形容詞性物主代詞(my, his, etc)或形容詞性指示代詞(this, that, etc)作限定詞, 其后的定語從句通常都是非限制性的:
　　Mary Smith, who is in the corner, wants to meet you.
　　Her mother, who had long suffered form arthritis, died last night.
　　All these books, which have been donated by visiting professors, are to be used by the postgraduates.
　　在非限制性定語從句中只能用who/whom指人, 用which指物,通常不用that替代.
　　My father, who had been on a visit to America, returned yesterday.
　　All the books, which had pictures in them, were sent to the little girl.
　　定語從句的引導詞
　　that, who, whom: 非限制性定語從句, 如果修飾人, 一般用who, 有時用that (作主語時用who較多). 如果關系代詞在從句中作賓語, 就應當用賓格 whom 或that, 但在大多數情況下都可以省略掉, 在口語中可用who代替whom.
　　Here is the man (whom) you’ve been looking for.
　　He is a man (that) you can safely depend on.
　　The people (who/that) you were talking to were Swedes.
　　There are some people here who I want you to meet.
　　但在介詞后只能用whom:
　　This is the man to whom I referred.
　　但在口語中一般都把介詞放到句子后面去, 這時可用that, 但省略時更多一些.
　　Have you met the person about whom he was speaking?
　　Have you met the person (that) he was speaking about
　　The girl to whom I spoke is my cousin.
　　The girl (who/that) I spoke to is my cousin.
　　限制性定語從句如果修飾“物”, 用關系代詞that的時候較多, 也有時用which.. 當這個代詞在從句中是用作賓語時, 在絕大多數情況下都是省略的, 特別是口語中(尤其是當被修飾的詞是all, everything等詞時):
　　Have you everything you need?
　　(Is there) anything I can do for you?
　　All you have to do is to press the button.
　　在介詞后只能用which, 在口語中一般都把介詞放到從句后部去, 這時可以用that, 但省略的時候更多一些:
　　The tool with which he is working is called a wrench.
　　The tool (that) he is working with is called a wrench.
　　This is the question about which we’ve had so much discussion.
　　This is the question (that) we’ve had so much discussion about.
　　定語從句一般是修飾名詞或代詞的, 但間或也可以修飾整個句子a), 或是句子的一部分 b), 引導詞用which:
　　They have invited me to visit their country, which is very kind of them.
　　The activity was postponed, which was exactly what we wanted
　　When deeply absorbed in work, which he often was, he would forget all about eating and sleeping.
　　She was very patient towards the children, which her husband seldom was.
　　whose: 在表示“．．．的”這個概念時, 可用所有格 whose; whose 用于指物, 有時可與of which交替使用, 通常的詞序是名詞詞組 + of which:
　　Is there anyone in your class whose family is in the northeast?
　　We had a meeting whose purpose was completely unclear. (…the purpose of which was…)
　　He’s written a book the name of which I’ve completely forgotten. (…whose name I’ve…)
　　of which前的名詞詞組也可以由some, any, none, all, both, several, enough, many, most, few以及基數詞擔任; 這些詞也能用在 of whom之前.
　　The buses, most of which were already full, were surrounded by an angry crowd.
　　It’s a family of eight children, all of whom are studying music.
　　關系副詞 when, where, why: 它們的含義相當于 at which, in which, for which, 因此它們之間有交替使用的可能.
　　The day when he was born…
　　on which he was born…
　　which he was born on…
　　The office where he works…
　　at which he works…
　　which he works at…
　　有時可用that替代關系副詞, 在口語中that 可省略.
　　Every time (that) the telephone rings, he gets nervous.
　　This was the first time I had serious trouble with my boss.
　　Do you know anywhere (that) I can get a drink?
　　This is the place (where) we met yesterday.
　　That is the reason (why) he did it.
　　在the way 后也可用that 替代in which, 在口語中that也可省略.
　　This is the way (that/in which) he did it.
　　That’s the way I look at it.
　　如果定語從句中謂語為 there is, 作主語的關系代詞也常可省掉:
　　I must make full use of the time there is left to me and do as much as I can for the people.
　　This is the fastest train (that) there is to Nanjing.
　　定語從句的簡化: 定語從句與不定式結構, -ing分詞結構, -ed分詞結構以及無動詞分句等有著轉換關系.
　　He was the only one to realize the danger (= who realized the danger).
　　The woman driving the car (= who was driving the car) indicated that she was going to turn left.
　　The man injured by the bullet (= who was injured by the bullet) was taken to hospital.
　　All the women present (= who were present) looked up in alarm.