问题补充：
To improve the quality of our products, we asked for suggestions had used the products.
A. whoever
B. who
C. whichever
D. Which
答案：
(答案→)A. whoever
B. who
C. whichever
D. Which
解析：考查名词性从句。本句结构为ask sb for sth 所以后面从句为宾语从句，从句中缺少had used the products的主语，即使用这个产品的人。故排除CD，根据句意可知，无论是谁使用了产品我们都会向他们寻求建议。故选A
