1.—He must be busy doing his homework right now.
A. that B. to C. so D. it
选C。I imagine so=I think so,
2. Mary had promised to give me a ticket for tomorrow. She failed, ____.
A. either B. though C. but D. too
3. When I got to the cinema, the film _____ for five minutes.
A. had begun B. has been on
C. has begun D. had been on
选D。电影开始了五分钟，for five minutes为一段时间要求谓语动词要用延续性动词，故A和C先排除，而从句的动作发生在主句动作之后。
4.---I wonder why Mr Green hasn’t showed up at the meeting yet.