It was playing video games that took the boy too much time that hehave spent learningA. c

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A. could
B. must
C. might
(答案→)D. ought to
解析：句意：就是玩游戏花了这个男孩太多的本应该学习的时间。Ought to have done“本应该做却没有做”，could have  done“本来可能会做”，must  have done“过去一定会做”，might have done“本来可能会做”，所以D。