如果存在齿轮偏心，则齿轮啮合频率仅存在（）时。
A.上边带频
B.下边带频
C.侧边带频
D.中边带频
参考答案：B
She will write to you as soon as she ______ to Bei-daihe . [ ]
A. arrives
B. reaches
C. gets
D. will get
简述业务网对传输网的要求。
