老顶初次垮落步距与其岩石性质及距地表垂深有关,一般在()米。
A.20~50
B.10~20
C.5~10
D.50~70
参考答案:A
如图所示,开关S1、S2闭合时电流表的示数为0.20 A,若通过灯L1的电流为I1,通过灯L2的电流为I1.则下列说法中正确的是
A.I1=I2=0.20 A
B.I1=I2=0.40 A
C.I1=0.20 A,I2=0
D.I1=0,I2=0.20 A
It was ________ that the PLA men got to the earth-strike area.
A.midnight
B.at midnight
C.until
D.for midnight