While _________the topic of music in class, all the students show great interest in it.
| A．discussed | B．discuss |
| C．discussing | D．are discussing |
The reason _______ he was absent from the meeting is_____ he suffered form a headache.
| A．what; because | B．for; that | C．why; that | D．when; because |
_______ to the sunlight for too long will do harm to your skin.
| A．Exposing | B．Exposed | C．Being exposed | D．Having exposed |
--- Congratulations!
---Thank you. If it hadn’t been for your help, we ____ in the experiment.
| A．will never succeed | B．wouldn’t have succeeded |
| C．mustn’t have succeeded | D．can’t have succeeded |
---You _________to our Mom like that. It was awfully impolite.
---You are right. I must have been crazy at that moment.
| A．mustn’t have talked | B．needn’t have talked |
| C．shouldn’t have talked | D．may not have talked |
Electric trains have now _______ steam trains in England.
| A．taken place | B．in place of | C．instead of | D．taken the place of |