what后谓语单复数
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What we need ________ good books.
A: 错误
is
B: 正确
are
C: 错误
be
D: 错误
is going to
what引导的主语从句，谓语可视表语而定，表语是单数名词，谓语动词用单数；相反，则用复数。
问题：主语从句不是谓语一律用单数吗？
若不是，那什么时候用单数，什么时候用复数呢？
其他的从句呢？
答：主语从句做主语，主句谓语动词的单复数需根据从句表示的单复数意义决定。
1．what引导的主语从句做主语
（1）通常情况下，由what引导的主语从句放在句首时，其后的谓语动词，按语法一致的原则用单数。
What she said is correct.
What caused the accident is not clear.
（2）当主句中的表语是复数形式，或what从句的谓语动词及其补足语均为复数形式时，主句的谓语动词应用复数。
What he gave me are five English books.
What are used as chief building materials today are steel and concrete.
（3）当what引导的主语从句是一个由and连接的并列结构时，应根据句意确定其表达的单复数意义，然后决定主句谓语动词的单复数形式。
What he says and acts does not concern me.
What he says and acts do not agree.
What I say and what I think are no business of yours.
2．由其它词引导的从句做主语时，谓语动词用单数形式。
Whether they will hold a party or not has not been decided.
Who is responsible for the accidents is not clear.
3．当同一个主语从句是由两个不同的引导词引导时，因为它表达的还是同一件事，因此，谓语动词一般用单数。
When and where we should hold the meeting has not been decided yet.
4．当主语是由两个由and连接的主语从句组成，通常表示的是两件不同的事情，主句谓语动词需用复数形式。
What you eat and how much you exercise are important factors in a weight loss program. What caused the accident and who was responsible for it remain a mystery to us.