可燃气体探测器调试时,应将发射器发出的光全部遮挡,探测器相应的控制装置应在()内发出故障信号。
A.100s
B.120s
C.150s
D.180s
参考答案:A
宇航员在地球表面上滑得一单摆的振动周期为2s,若他将这一单摆带到某星球表面上,测得其振动周期为4s,忽略空气阻力,已知该星球的半径与地球半径之比为,设地球表面重力加速度为g,星球表面的重力加速度为,地球质量为,星球质量为,则 ( )
A.
B.
C.
D.
______Jay Chou hums or sings,his fans love him and his songs. [ ]
A. Whatever
B. Whenever
C.Whichever
D. No matter