二、对过去情况的后悔、遗憾或责备
1.could have done用于肯定句,表示“本来能够做某事而没有做”。 He could have passed the 2017 Entrance Examination to the College,but he was too careless. 本来他能够通过2017年高考,但是他太粗心。 2.should have done表示“本来应该做,而实际没做”。 I really regret wasting the hours when I should have studied hard,but it is too late. 我真的很后悔该努力学习的时候浪费了太多时间,但现在太晚了。