当关系代词在句子中作表语时。 He is not the man that he used to be。2。 以下情况不能用关系代词 that。1) 在非限制性定语从句中,who, whom指人,which指物,不能用关系代词 that。 The boy made the same mistake again and again, which made his teacher rather angry。2) 在介词后面不能用关系代词 that,指物时用 which,指人时用 whom (不用who)。 The house in which he lives is not far from here。 The man to whom my mother is talking is my teacher。 3。 当先行词是 place(或其它表示地点的词), time(或其它表示时间的词), reason时。