They can't have been doing thier homework.have been 是现在完成时,但是后面do为什么要变成doing?

They can't have been doing thier homework.have been 是现在完成时,但是后面do为什么要变成doing?
They can't have been doing thier homework.这句话 have been 是现在完成时,但是后面do为什么要变成doing?为什么不用do呢?还有They must have been playing in the garden.为什么也用playing,而不用play呢,
英语人气:767 ℃时间:2019-11-07 22:23:33
优质解答
现在完成时结构 have/has+P.P.
现在完成进行时结构 have/has +been+doing
此句在现在完成进行时 前加上情态动词,can't have been doing 表示一种语气较肯定的推测.意为那时不可能在做某事
我来回答
类似推荐
请使用1024x768 IE6.0或更高版本浏览器浏览本站点,以保证最佳阅读效果。本页提供作业小助手,一起搜作业以及作业好帮手最新版!
版权所有 CopyRight © 2012-2024 作业小助手 All Rights Reserved. 手机版