在警衔的设置中，( )是初级警官。
A．警监和警督
B．警督和警司
C．警监和警员
D．警司和警员
参考答案：D
Could you please tell me _____? [ ]
A. where the Grand Central Station is
B. how far the Grand Central Station was
C. how can we get to the Grand Central Station
D. when was the Grand Central Station built
用焊条电弧焊焊接Q235钢时，如果选用焊接电流为160A，电弧电压是25V，焊接热输入不超过28KJ／cm时，求此时的焊接速度应选用多少（已知焊条电弧焊的热效率η=0、7）？
