It was computer games that cost the boy a lot of time that he ought to have spent on his

问题补充：

It was computer games that cost the boy a lot of time that he ought to have spent on his lessons.

A. to have played

B. playing

C. played

D. having played

答案：

A. to have played

(答案→)B. playing

C. played

D. having played

解析：此句是强调句型，强调句子的主语playing computer games。