what做主语时,后面的动词用单数还是复数

what做主语时,后面的动词用一般用单数的较多.如果后面接的表语是名词,那么谓语be根据表语决定.如：
What you said is important.
What we do now is (to) study hard.
What we need is knowledge.
What they want are some books.