A city,whether big and small,should be clean. Only when we live in a clean city we live a happy life. As we know,a clean city,that disease may be reduced and people's health may be better,are good both to our mind and body. No one believes people lived in a dirty city with waste everywhere can live happy. However,as more and more people moving into our city,it is not easy to keep our city clean. Beside,some factories will pour waste into the air,the river and onto the ground,making it is hard to keep our city clean. To make our city the better place to live in,we still have a lot to do.