我厂膨胀空气换热器采用（）作为冷源.
A.氧气
B.氮气
C.污氮气
D.空气
参考答案：A
Success in life doesn't happen __________. It's the result of devoting your time and energy to what
you've set out to do.[ ]
A. by force
B. by design
C. by accident
D. by choice
低压隔爆开关的触头（铜触头）磨损至原厚度的（）、超行程压力低于规定值时，应更换接头。
A、二分之一
B、三分之一
C、四分之一
