用place短语的适当形式填空。

1. A little gratitude would be ____.

2.I' m at a loss what to do next. What would you do (if you were )____ ?

3. Plastics have ____ manyother materials.

4.  We use plastics _____ many other materials.

5. While the manager was on holiday, he ___.

什么情况下应紧急停运离心式空压机？