在定语从句中 what是不可能出现的如果在选择题中出现what肯定是错误但定从中有种情况：all that=all=what(而此处的what多是主语从句)e.g.All that i've done is for you. =All i've done is for you. =What i've done is for you.P.S.当that在定从中充当主语时，不可省
