The boy won the first prize is called Roy.A. whenB. whomC. whoD. which

问题补充：

The boy won the first prize is called Roy.

A. when

B. whom

C. who

D. which

答案：

A. when

B. whom

(答案→)C. who

D. which

解析：本题中修饰boy是一个定语从句，修饰人的用who，在从句中做主语，故选C。