根据汉语意思提示完成句子。
1. By 2008, the environment here will be ____________ (更加舒适).
2. Do you know what the ____________ (目的) of learning English is?
3. In our country, we will never _____________ (挨饿)
4. In the past, each family had _____________ (至少) three or four children in our country.
5. I think ____________ (空气污染) is the most serious problem in the world.
