It was playing computer games cost the boy plenty of time he ought to have spent doing his

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(答案→)A. that; that
B. which; that
C. which; when
D. that; when
解析：这题考查强调句，强调的是playing puter games，第二空考查定语从句，先行词是plenty of time，定语从句中缺乏宾语用that引导句意是：就是玩电脑游戏花了男孩本来应该花来写作业的时间。选A。