The river smells terrible.People must --- dirty things into

1 have thrown / put / poured -------你的句子本来就是主动语态.
2 stop putting / pouring / throwing
再问： 为什么stop 后面不加from?
再答： 你好。如果是- - -- from - -- -，就必须是： we must stop people from putting dirty things into the river stop sb from doing sth ------不让某人做某事