连续传动的条件
参考答案：
一对齿轮必须满足正确啮合条件，而且重合度ε＞1。
He pretended _______ me when we met in the street.
A．not to know
B．not to be knowing
C．not having known
D．not knowing
接地有哪些种类？其应用范围？
