选择题: ---- Lily, nice to see you ! ______ to England ?-

题目内容:
 ---- Lily, nice to see you ! ______ to England ?
---- Yes. And I will come back in a week. ( )(本题1.5分)
A. Have you gone
B. Are you going
C. Have you been
D. Did you go
参考答案:

10.边际成本低于平均成本时( )(本题2.0分)A. 平均成本上升B. 平均可变成本可能上升也可能

10.边际成本低于平均成本时( )(本题2.0分)A. 平均成本上升B. 平均可变成本可能上升也可能下降C. 总成本下降D. 平均可变成本上升

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