A: Look! The river clean before, but it's very now. Let's do something（一些事情）.

B: Good idea. But what should we ?

A: We should put trash into the river.

B: OK. From now on, I throw the trash into the trash.

A: I think we should pour（倒） water into the river.

B: Great! I hope（希望）we can the river clean.