To improve the quality of our products, we asked anyone had used the products for suggest

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A. whoever
(答案→)B. who
C. which
D. whichever
解析：考查定语从句。本定语从句的先行词是anyone，定语从句中缺少主语，故使用who指代先行词anyone在句中做主语。句意：为了提高产品的质量，我们想那些使用过我们产品的人征求建议。故B正确。