) something must be done to stop the pollution. (人類必須采取一些措施來制止污染, they pour dirty water in to rivers.(更糟糕的是他們排放污水到河流里, the last drop of water will be a tear-drop of us.( 如果我們不節(jié)約水,我們才過得幸福開心,)the amount of water which is suitable to drink is less and less.