机车粘着重量Pμ与动轮与钢轨间粘着系数μ的乘积即为（）。
A、机车粘着牵引力
B、机车牵引力
C、牵引力
D、被动力
参考答案：A
—How do you usually keep in touch with your friends, by email or letter？
— .
A．None
B．Neither
C．Any
D．Either
—When did you live in Beijing, Mary?
— I lived there____ 2008 to 2013.
A．on
B．from
C．for
D．of
