问题
选择题
It was very kind of you to do the washing up, but you _______ it.
A．mustn't have done
B．wouldn't have done
C．mightn't have done
D．didn't have to do
答案
D
考查情态动词和虚拟语气的用法。don't have to do sth.“不必做某事”。也可以说needn't have done it。
2SO3（g）＋196．64kJ。达到平衡时，实验室测得放出的热量为314．3kJ，则SO2转化率最接近于[ ]