that在引导宾语从句、主语从句、定语从句以及同位语从句时,都被称之为“关系代词”么?

that在引导宾语从句 ,可以省略。eg：he said (that) he was a student。主语从句我很少见that引导,一般为what,不能省略。what he said was a good idea。what he said是一个主语从句。that引导同位语从句时,不能省略。I can't stand the terrible noise that she is crying loudly。she is crying loudly是一个完整的句子,并不是一个修饰语,它the terrible noise的内容,两者都是指一个东西。that引导定语从句时,可以省略。而which 只有在做宾语时可以省略,其余不能省略。she wa dressed in a bezutiful skirt (that) was printed two tigs。was printed two tigs 是用来修饰a bezutiful skirt,做其定语的。其实以上都可以称之为关系代词,只是搞清楚其用法非常重要,最长考的是定语从句,其次是同位语从句,宾语从句有时候也有,主语从句主要是考what,