低压隔爆开关的触头（）磨损至原厚度的（）、超行程压力低于规定值时，应更换触头。
A.1/2
B.1/3
C.1/4
参考答案：B
Old people need special care in winter, as they are very______ to sudden change of the weather.
A．sensitive
B．painful
C．attractive
D．familiar
试述队列研究的设计思路。
