句的关系十分密切，不可用逗号将主句隔开。 e.g. (1)This is the best film that I have ever seen.
(2)The teacher told me that Tom was the only person that was reliable.
2)非限制性定语从句是先行词的附加说明，如果省去，也不致影响主句的意思。它和主句之间往往用逗号隔开。
e.g. (1)Last night I saw a very good film, which was about the Olympic Games.
(2)I like to chat with John, who is a clever fellow.
2.关系代词在定语从句中作介词宾语时，介词既可置于从句之首，亦可置于从句之末。但以置于从句之首较为正式。
e.g. (1)This is the book
for which you asked.(关系代词用作介词for的宾语，介词置于从句之首)
亦可：This is the book which you asked for. (2)This is the house in which LuXun once lived.
亦可：This is the house which LuXun once lived in. 实例：
(1)Model Test 1:p31:
14.She was always speaking highly of her role in the play, ( ), of course, made the others unhappy. A)who B)which C)this D)what
(2)Model Test 3:p51: 16.The gentleman ( ) you told me yesterday proved to be a thief.
A)who B)about whom C)whom D)with whom
五． 情态动词
