题目

They must have done their homework yesterday,____?
这个句子的反意疑问句为什么是didn't they呢?

提问时间：2020-09-30

答案

must have done 表示的是对过去动作进行推测,其反义疑问句的构成有两种：didn't .../wasn't(weren't) .../haven't(hasn't)...这两种形式的选择取决于句子中的时间状语.比较一种简单的方法是：不把它看成是推测,就把它看成是一种事实.
比如：He must have been to Beijing,hasn't he?
You must have been late for school yesterday,wasn't you?
换句话说,用过去时还是用现在完成时来进行反问的区别,等同于过去时和现在完成时的区别.
又如：It must have rained last night,didn't it?