施工升降机的接地必须牢固可靠，其接地电阻不大于（）
A.4
B.8
C.10
D.20
参考答案：A
—I just want to know. Please tell me, how much do you make an hour?
—If you_____ know, I make $20.00 an hour.[ ]
A. will
B. shall
C. must
D. need
初产妇的第二产程约为：
A．11～12小时B．6～8小时C．1小时D．1～2小时E．5～15分钟
