what引导的主语从句谓语动词单复数由主句谓语动词后的名词决定你例如上面的句子，因为名词是twobooks，是复数，所以谓语动词用are希望能够帮助到你
一般不用原形,如What I want to do is to help him.what I want to get is his love.What I want to know is whether he is safe.
不一定
