1 . I appreciate your________ (ring) back to me so timely. （所给词的适当形式填空）

3 . Hearing that my good friend was out of danger, I __________（如释重负地挂断了电话）。（根据汉语提示完成句子）

4 . 用方框中所给的动词短语的正确形式填空。
leave sb alone； turn around；   test out；set aside；   ring up；   smooth away
1. How many people __________________ while I was out?
2. The model must ____________________ before we put it into mass production.
3. __________________, I saw an old friend of mine, whom I haven’t seen for years.
4. She is very upset. _______________ for a few minutes.
5. It’s time for us _________________ our differences and work together for a common purpose.
6. There are still a few problems to be ___________________ before we can complete the project.

5 . After the clock _____ twelve, the students walked out of the lecture room.

A．beat

B．hit

C．struck

D．rang

6 . He promised _____ back in a few minutes.

A．to ring

B．ringing

C．rang

D．to be ringing