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选b这是非限定性定语从句的用法非限制性定语从句 1。 which引导的非限定性定语从句作用是说明前面整个句子的情况或主句的某一部分 2。当先行词是专有名词、 才 物主代词或指示代词所修饰时,其后的定语从句通常是非限制性的,例如： Charles Smith, who was my former teacher, retired last year。 查理·史密斯去年退休了,他曾经是我的老师。 My house, which I bought last year, has got a lovely garden。 我去年买的的那幢房子带着个漂亮的花园。 This novel, which I have read three times, is very touching。 这本小说很动人,我已经读了三遍。 3。非限定性定语从句可将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数,例如： He seems not to have grasped what I meant, which greatly upsets me。 他似乎没抓住我的意思,这使我心烦。 Liquid water changes to vapor, which is called evaporation。 液态水变为蒸汽,这就叫做蒸发。 4。 有时as也可用作关系代词 5。 在非限定性定语从句中,不能用关系副词why和关系代词that,而用who, whom代表人,用which,whose代表事物,如果需要用why,可用for which代替。；