—I hear Robert has gone to Harvard University for his masters degree.—Oh how nice!Do you

问题补充：

—I hear Robert has gone to Harvard University for his masters degree.

—Oh,how nice!Do you know when he?

A. was leaving

B. left

C. had left

D. has left

答案：

A. was leaving

(答案→)B. left

C. had left

D. has left

解析：由上下文可知此处when暗含一个过去时间，故应用一般过去时态。