炸药在井下30m处爆炸,井口检波器记录的井口时间为20ms,波传到地震面的速度是()。
A.150m/s
B.1500m/s
C.300m/s
D.3000m/s
参考答案:B
—Who _______ from Canada?
—Nancy and I ________. [ ]
A. are come; do
B. is come; does
C. comes; do
D. is; is
检波器的阻尼程度只对检波器的振幅有显著的影响。