—Mum, could you buy me a dress like this?  

—Certainly, we can buy ______ one than this, but ______ this.    [ ]

A. a better; better than  

B. a worse; as good as

C. a cheaper; as good as  

D. a more important; good as

袋收尘器的箱体：主要是（）、（）及气路元件之用，并制成全密闭形式，清灰时，压缩空气首先进入箱体，并冲入各滤袋内部。