问题补充：
---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; not as good as
答案：
A. a better; better than
B. a worse; as good as
(答案→)C. a cheaper; as good as
D. a more important; not as good as
解析：考查比较级和as+形容词+as的用法，比较级表示两者之间的比较，as+形容词+as表示同级比较，句子意思“我们买一个比这件更便宜的，但是和这件一样好”，所以选C
