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

问题补充：

It was computer games that cost the boy 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：本句是一强调句式，被强调部分在句中作主语，由动名词充当。