Every day large quantities of waste water______into river without being cleaned.

C.are poured

为什么谓语动词要用are?

因为,quantities of +名词时,后面的谓语的单复数是看quantities 而不是"名词".就是说只要用quantities of 后面的谓语就要用复数.而且,这里用被动，所以是are poured.