I wonder whether the soldier is one of those who abroad to keep peace.A. has been sentB.

问题补充：

I wonder whether the soldier is one of those who abroad to keep peace.

A. has been sent

B. have been sent

C. have sent

D. has sent

答案：

A. has been sent

(答案→)B. have been sent

C. have sent

D. has sent

解析：考查主谓一致：句意：我想知道是否这个士兵是要被派出国维和的士兵之一。Who引导的是定语从句，定语从句的谓语和先行词保持一致，这个定语从句的先行词是those，谓语是复数，还有soldier和send是被动关系，所以选B。