当先行词是all, everything, nothing, something等不定代词时，定语从句中只能用that。例句：All that glitters is not gold.当先行词被序数词、最高级、next, last, only等修饰时，定语从句中只能用that。例句：This is the only book that I have.当先行词是不定式、分词或从句时，定语从句中只能用that。例句：He had nothing to say that could help.当先行词被all, any, few, little, many, much, no, some等词修饰时，定语从句中只能用that。例句：There is little doubt that he will win.