It was playing computer games that cost the boy plenty of time that he spent doing his le

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A. might have
B. should
(答案→)C. ought to have
D. could
解析：考查情态动词。根据句子，指的是过去的情况，所以要用情态动词加完成时态表过去本应该做而实际没做的事。might have done,本可以做某事；ought to have done本应该做而实际没做。句意：玩电脑游戏花费了这个男孩大量的时间，他本应该把时间用在功课上。所以选C。