题目内容：

Is that old man _ you often help with his housework.选哪一个
A./ B.as C.why D.the one

优质解答

D,这是定语从句的只是,先把句子变为肯定句,只能是That old man is ______ you often .这个句子中is缺表语（同时又是后面定语从句的先行词）,后面的help缺少宾语,所以应该用the one who/that,做宾语时that'或who...