— Which dress do you like best Madam ?— Sorry I can’t decide now .A. to buy which one

问题补充：

— Which dress do you like best , Madam ?

— Sorry , I can’t decide now .

A. to buy which one

B. buy which one

C. which one to buy

D. which I should buy it

答案：

A. to buy which one

B. buy which one

(答案→)C. which one to buy

D. which I should buy it

解析：句意：你最喜欢哪一件衣服，夫人？对不起，我现在不能决定买哪一件。疑问词可以放在动词不定式之前，和其一起构成动词不定式短语。所以选C。