Question

It was playing computer games that cost the boy plenty of time that he _______ have spent doing his lessons.?
A.might  B.must C.ought to D.could

Answer 1

C

ought to/should have done表责备，意为“应该做（而未做）”，might have done表示“可能已经做了”。must have done 表示“一定做了，”could have done 指“本来能做而没有做”。
根据句意“正是玩电脑游戏花了这男孩大量本应花在功课上的时间”可知应该用ought to。