用括号内所给动词的适当形式填空。

1. After a knock at the door, the child heard his mother's voice _____ (call) him.

2. It's no good _____ (waste) strength in shouting.

3. Our group is mainly concerned with bird _____ (conserve) in coastal areas.

4. He felt embarrassed with so many eyes _____ (focus) on his clothes he was wearing.

5. The children talked so loudly at dinner table that I had to struggle _____ (hear).