Only when he failed the exam that he didn’t work hard. (原创)A. he regrettedB. did he regre

问题补充：

Only when he failed the exam that he didn’t work hard. (原创)

A. he regretted

B. did he regret

C. had he regretted

D. does he regret

答案：

A. he regretted

(答案→)B. did he regret

C. had he regretted

D. does he regret

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