Ⅰ. 根据句意及首字母提示完成单词（10分）
1. Paper can be r_______. We’d better not throw it away.
2. It is important to try to save e_______.
3. If we don’t protect our e_______, the earth will be destroyed.
4. Our teacher tells us to collect r_______ plastic bags.
5. Gold, silver and iron are all m_______.
