The course normally attracts 20 students per year up to half will be from overseas.A. in

问题补充：

The course normally attracts 20 students per year, up to half will be from overseas.

A. in which

B. of whom

C. of which

D. for whom

答案：

A. in which

(答案→)B. of whom

C. of which

D. for whom

解析：句意：这个课程正常一年吸引20个学生，其中有一半是来自海外。这里使用了定语从句，先行词是20 students，定语从句中是half of the 20 students will be from overseas.所以用of whom引导定语从句，选B。