Question

must表推测时 must do 和must have done的区别

Answer 1

must表推测时 must do 和must have done的区别
must表推测时 : 必定，一定

The light is still on, so he must be at home. 灯还是亮的，他一定在家。

The light was out. They must have gone to bed. 灯都熄了，他们必定睡了。

注意：1. must表示推测时的否定式是can’t或couldn’t(不可能) ，因为must只用于肯定句，语气很强。2. 若对过去情况的推测用must have加过去分词。