Since there is water everywhere,last night

问题描述:

Since there is water everywhere,last night
 Since there is water everywhere,        last night.   a.it must have been rained    b.it must have rainedc.it must be raining         d.it must rain中文意思,选择哪一个,为什么?

选B must have done 肯定做过某事或发生过某事