I first met Mr. Smith in America. He at Stanford University then.A. studiedB. has studied

问题补充：

I first met Mr. Smith in America. He at Stanford University then.

A. studied

B. has studied

C. is studying

D. was studying

答案：

A. studied

B. has studied

C. is studying

(答案→)D. was studying

解析：由关键词：then推出过去进行时。