Long time ago, our world was very beautiful. There were trees, flowers and rivers. It was very clean and tidy. 1 . We are living in a polluted environment, which is bad for out earth. 2 .The public has been calling for actions against pollution. Scientists have told us to protect out environment, 3 .
The earth is our only home. We should make it comfortable for ourselves and for our children in the future. Now nearly all of the countries are trying their best to stop pollution. Although they have done much, the progress is slow, 4 . No matter how difficult it is, we should try our best to fight against pollution. By working together, 5 .
根据短文内容，从方框中选出能填入空白处的最佳选项，补全短文。（5分）
