1. 用方框内短语的适当形式填空

at large; safe and sound; occur to; keep one's head; hold on to; in case; to one's relief; a series of; at the same time

1. （1） Space travel can be so delightful but invisibly dangerous.
3. （2） Mobile phone users have developed symbols to show how they feel.
5. （3） , the accident caused little damage to his health.
7. （4） The old man the back of the chair to stop himself from falling.
9. （5） I took my driving license with me on holiday, I wanted to hire a car .
11. （6） Two days later, the missing children returned home .
13. （7） Faced with this situation, a good idea suddenly him.
15. （8） When you are faced with challenges, you should .
17. （9） I think the chances of getting reforms accepted by the community remain extremely remote.