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).