制动轮与电机轴联接时，用止动垫圈将螺母锁住属（）。
A、磨擦防松
B、机械防松
C、自锁防松
参考答案：B
—Jane, which color do you prefer, red or blue? —______. I prefer to buy a green one.
A．Either will be OK
B．Both will be OK
C．To be honest, neither
D．Generally, I’m not sure
麻疹减毒活疫苗的初种年龄为_______个月以上易感儿。复种年龄为_____岁。
