--- I hear Robert has gone to Harvard University for his master’s degree. --- Oh how nice

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

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