what,when,why,who,how 在句子中间出现,表示它引导的不是一个独立问句,而是一个从句.例如
I don't know what he did.我不知道他干了什么.
I don't know when he did it.我不知道他是什么时候干这件事的.
I don't know why he did it.我不知道他为什么这么干.
I don't know who did it.我不知道是谁干的.
I don't know how he did it.我不知道他是怎么干的.