1.非限制性定语从句不可用that引导， 在非限制性定语从句中用who(作主语) / whom(作宾语)指人，用which(作主语 / 宾语)指物， 用whose作定语(指人 / 物)。
例如：The famous basketball star, who tried to make a comeback, attracted a lot of attention.这位试图打反击的著名篮球明星吸引了众人的关注。The film, whose director is an old man, is very instructive.这部电影很有教育意义， 它的导演是位老人。
2.关系代词在非限制性定语从句中作宾语时不可省略，若指人时，只用whom，不用who。例如：York, which I visited last year, is a nice old city.我去年访问过的约克是个古老而美丽的城市。Please give the book to Jessica, whom we met in the hall just now.请把这本书交给杰西卡，就是刚才我们在大厅里遇到的那位。
3.非限制性定语从句不可用why引导， 需用for which替代why。例如：None of us accepted the reason he explained, for which he was absent.我们没有一个人接受他所解释的缺席的理由。
