could have done的各种用法(在肯定句,否定句,疑问句中)

Question

如题所述

Answer 1

“could+have+done”是虚拟语气，表示对过去事情的假设，意思是本来能够做某事而没有做。
He could have passed the exam, but he was too careless. 本来他能够通过考试，但是他太粗心 　疑问句：①Could you have done the exercises?　　你可能做完练习吗？　否定句②They couldn’t have finished the work so soon.　　他们不可能这么快就做完了。

Answer 2

could have down为固定结构，意为“本该做但实际未做，”它得疑问句就是把Could 提前，Could ＋主语＋have done。