WalMart the world's largest retailer(零售商) sells in three months the numbertwo retailer

问题补充：

WalMart，the worlds largest retailer(零售商)，sells in three months the numbertwo retailer Home Depot sells in a year.

A. that

B. which

C. when

D. what

答案：

A. that

B. which

C. when

(答案→)D. what

解析：在宾语从句sells后缺宾语，故用what连接。