Milk bottles need cleaning thoroughly before they are used again,___ they?don't mustn't aren't

问题描述:

Milk bottles need cleaning thoroughly before they are used again,___ they?
don't
mustn't
aren't

aren't

应该用aren't,表被动,牛奶杯在再次使用之前要被彻底地清理干净,不是吗?

don't
Milk bottles need cleaning thoroughly before they are used again,don't they?