根据句意及首字母提示补全单词。

1. When I found him, he was cutting his hair in a b         shop.

2. No one knew what h         before they came to the museum.

3. While she was in the kitchen, she heard someone s         for help.

4. They were talking to some police o         in the park at that time.

5. Some children were s         when they saw the terrible animal.

以一定的初速度竖直向上抛出一个小球，上升的最大高度为h，运动中空气阻力的大小恒为f,则小球从抛出点到再回到原抛出点的过程中，空气阻力对小球做的功为

A．0

B．-fh

C．-2fh

D．-4fh