--Shall Mary come and play computer games?
--No,__________ she has finished her homework.
A. when B. if C. unless D. once
--Shall Mary come and play computer games?
--No,__________ she has finished her homework.
A. when B. if C. unless D. once
C
本题只要理解了句意就能很容易地选出unless。句意为：“玛丽要来打电脑游戏吗?”“不，除非她完成了作业。”