根据句意和汉语注释，写出单词的正确形式。
1. _______ (污染) air does harm to our health. It’s necessary to keep the air fresh and clean.
2. Our success was far _______ (超过) what we thought possible.
3. This kind of disease _______ (传播) so quickly that it drew the government’s attention.
4. The man kept remembering English words every day until he was in his _______ (四十).
