根据句意和首字母提示补全单词.

1. Don't w________ water. Please turn off the cock after you wash your hands.

2. Gold, silver and iron are all m_______.

3. It's more and more important for everyone to save e_______ now.

4. Air p_______ is quite harmful to our health.

5.The students from a green school are helping collect waste paper and bottles for r________.