问题补充：
Look! There is a whole crowd of people over there．Go and see what and if it is a bargain，buy it．
A. is selling
B. has been selling
C. is being sold
D. has been sold
答案：
A. is selling
B. has been selling
(答案→)C. is being sold
D. has been sold
解析：句意：看！那边有一群人，去看看在卖什么，如果便宜就买。根据句意是说话的时候正在卖什么，用现在进行时，而且what和sell是被动关系，用现在进行时的被动语态，所以选C。
