题目内容：

needn't do和 didn't need to do的区别
The students ______ to school yesterday as the local government announced that all the school classes were to be canceled due to the terrible typhoon.
A didn't need to go B needn't go
但是AB都表示不必做,而且都没有做过.B为什么不对?

优质解答

A didn't need 表示“过去不必”
B needn't go 表示“将来不必“
此题中,有时间状语”yesterday“,因此要用过去式,故选A