—I’m sorry I have failed again in the math exam．—？You’ve been working hard at the subject．

问题补充：

—I’m sorry I have failed again in the math exam．

—？You’ve been working hard at the subject．

A. How

B. How come

C. Why not

D. When

答案：

A. How

(答案→)B. How come

C. Why not

D. When

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