___the old man's sons wanted to know was___the gold had been hidden.
What the old man's sons wanted to know was___the gold had been hidden.
B.where ; C.that ; D.if
我想知道为什么这里不能用that呢?我知道这里答案是where,if的话是因为 这一句句子其实是一句表语从句,而if是不可以引导表语从句的.而where,whether,that都是可以引导表语从句的.那么我想知道为什么不可以选择that呢?