根据句意和首字母提示完成下列句子。 

1. The sun sets (落下) in the w        .  

2. They are swimming at the p        .  

3. The little boy is playing with a t        .  

4. Tina is s         in the supermarket now.  

5. Some a         are for children. Some are for young people.

简述乐音与噪音的区别。