) something must be done to stop the pollution. (人类必须采取一些措施来制止污染, they pour dirty water in to rivers.(更糟糕的是他们排放污水到河流里, the last drop of water will be a tear-drop of us.( 如果我们不节约水,我们才过得幸福开心,)the amount of water which is suitable to drink is less and less.