在圆柱齿轮传动中，材料与齿宽系数、齿数比、工作情况等一定情况下，轮齿的接触强度主要取决于（）大小。
A.模数
B.齿数
C.压力角
D.中心距
参考答案：D
It is not _____ that Sanlu has been connected to a scandal involving milk powder, according to China Daily.
A．for the first time
B．the first time
C．first time
D．in the first time
马蒂斯
