Mary is the only one of the students in our class who to the Great Wall so far.A. isB. ha

问题补充：

Mary is the only one of the students in our class who to the Great Wall so far.

A. is

B. has been

C. are

D. had been

答案：

A. is

(答案→)B. has been

C. are

D. had been

解析：考察时态。句意：玛丽是我们班唯一的一个目前曾经到过长城的人。可知从句中描述的是先已经完成的动作，故用现在完成时态。选B。