如果先行词是指人的不定代词someone，anybody等作先行词，作主语用who，作宾语用whom。作主语用who . ；
只能用that
定语从句只能“that”引导的情况：1、先行词是最高级或被最高级修饰.This is the most interesting book that l have ever read.2、先行词是序数词或被序数词修饰.The second foreign country that l expect to visit is Greek.3、先行词是不定代词时，如"；all、few、little、much、anything、nothing、something"；This is the very good dictionary that I want to buy.4.、先行词既有人又有物时Can you remember the scientist and his theory that we have learned?5、先行词被“only”、“the every”、“no”、“one of”等修饰He is the only person that l want to talk to.6、在以“which”、“who”、“whom” 引起的问句中，为避免重复，常用"；that"；Who is the man that is standing there?Which is the T-shirt that fits me most?7、“there be”句型中8、先行词在主句中作表语，或者关系代词本身作从句的表语时宜用“that”“that”在作宾语时可省略
不定代词后面跟who还是whom
要看不定代词在句子中所做的成分。
如果说不定代词表示人，并且在句子中作主语，那应该用主格who，如果说不定代词在从句中做的是宾语或表语，补语等，应该用宾格，whom。
