螺口灯头的螺纹应与（）相接。
A、零线
B、相线
C、地线
参考答案：A
The Class 3 and Class 1 runners both ran very slowly.
_____ of them ran faster than the Class 2 runner.
A. Either
B. Nobody
C. None
D. Neither
复式交分道岔两接触线相距500mm处应等高，允许高差（）mm。
A、5
B、10
C、20
D、30
