从句主语时谓语用单数还是复数
当从句用作主语时，主句的谓语动词通常用单数。如：
That he is still alive is a wonder. 他还活着，真是奇迹。
That we shall be late is certain. 我们要晚了，这是确定无疑的。
What she lacks is experience. 她缺的是经验。
What he says is not important. 他说的话并不重要。
Whatever she did was right. 她做的一切都是对的。
When we arrive doesn’t matter. 什么时候到没有关系。
How it was done was a mystery. 这是怎样做的是一个谜。
How this happened is not clear to anyone. 这件事怎样发生的，谁也不清楚。
Whether it will do us harm remains to be seen. 是否对我们有害还要看一看。
Who he is doesn’t concern me. 他是谁与我无关。
Whoever breaks this law deserves a fine. 违反本法者应予以罚款。
若用作主语的是what引导的从句，且其后为系表结构，此时需注意以下两点：
1. 若表语为复数，主句谓语通常用复数。如：
What I want are details. 我要的是细节。
What is needed are rational and firm actions. 所需要的是合理的坚决的行动。
2. 若what从句中的what表复数意义，则主句谓语动词要用复数。如：
His muscles were wasting away, and what were left were flabby. 他的肌肉正在消耗，所剩下的就是松弛的皮肉。