—Will Mr. Brown come and play computer games?—No he has finished his homework. A. whenB.

问题补充：

—Will Mr. Brown come and play computer games?

—No,he has finished, his homework.

A. when

B. if

C. unless

D. once

答案：

A. when

B. if

(答案→)C. unless

D. once

解析：句意：-----布朗先生会来玩电子游戏吗？----不，除非他已经完成了他的作业。when 当……的时候；if 如果；unless 除非，如果不；once一旦……就。 故选C。