1. at the bottom of the river 在河床底部
2. be full of the rubbish 充满了垃圾
3. throw litter into the river 把垃圾扔入河中
4. play a part in cleaning it up 尽一份力把它清理干净
6. fill the air with black smoke 使空气中充满了黑烟
7. cut down air pollution 减少空气污染
8. make a difference 产生影响
11.use public transportation 使用公共交通
12.recycle books and paper 回收书和废纸
13.use paper napkins 使用纸巾