将测量接地电阻极E使电位测针P1和电流探测针C1沿直线彼此相距（）米，然后进行测量。
A.20
B.30
C.50
D.80
参考答案：A
排放瓦斯时，每次启动局部通风机后，均应检查局部通风机是否有循环风。
The teacher said ______ wanted to go to the cinema must be there before 6:00.
A．those who
B．that
C．who
D．which
