6.關系代詞在限制性定語從句中�？梢允÷�,一般有以下幾種情況:

　　1) 關系代詞在從句中作直接賓語時，在大多數情況下可以省略。

　　This is something (that) you must always keep in mind.

　　The man (whom) you just met is our manager.

　　關系代詞作介詞賓語時，介詞位于句尾時關系代詞可以省略;介詞位于關系代詞之前時則關系代詞不能省略。

　　This is the room (which) Churchill was born in.

　　This is the room in which Churchill was born.(which不可省略)

　　2) 關系代詞作主語時一般不能省略，但如果關系代詞在由there … be存在句構成的定語從句中作主語時常可省略。

　　This is the only book (that) there is on this subject.

　　The old professor made full use of the time (that) there was left to him to continue his research.

　　3) 在way后面的定語從句中in which或that通常省略。

　　That’s the way (that/in which) I look at it.

　　I don’t like the way (that/in which) you laugh at her.

　　7.非限制性定語從句

　　非限制性定語從句修飾先行詞或整個主句，起補充說明的作用，如果省略掉，原句句意仍保持完整。非限制性定語從句要用逗號與主句隔開，其引導詞不能用that。非限制性定語從句屬于正式語體。經常考到的非限制性定語從句有以下三種。

　　1) 由which、as引導的非限制性定語從句。which、as代表整個主句。

　　He said that he had never seen her before, which was not true.

　　China is still a developing country, which is known to all of us.

　　2) 由 “介詞+關系代詞”引導的非限制性定語從句。

　　He sent her a letter, in which he said that he was sorry for what he had done to her.

　　He failed to pass the exam, because of which his parents scolded him.

　　4) 由 “數詞、代詞或名詞+of +關系代詞”引導的非限制性定語從句。

　　He had three sons, one of whom was my son’s classmate.

　　There are about twenty students in this course, most of whom are freshmen.

　　They are two different words, the spellings of which are easily confused.