To improve the quality of our products we asked for suggestions had used the product.A.

问题补充：

To improve the quality of our products, we asked for suggestions had used the product.

A. no matter who

B. who

C. whoever

D. whichever

答案：

A. no matter who

B. who

(答案→)C. whoever

D. whichever

解析：考查whoever引导宾语从句，whoever引导宾语从句相当于anyone who，做ask的宾语，句意：为了提高产品的质量，我们向用过产品的人征求建议。选C。