MF/HF单边带无线电话通信,其电波采用()传播.
A.天波
B.地波
C.空间波
D.A+B
参考答案:D
如图所示为某质点作直线运动的v-t图象,关于这个质点在4s内的运动情况,下列说法中正确的是
A.质点始终向同一方向运动
B.4s末物体离出发点最远
C.加速度大小不变,方向与初速度方向相同
D.4s内通过的路程为4m,而位移为零
30.It is reported that there will be a heavy rain tomorrow; _____ the hike would be put off.
A.in any case
B.in which case
C.in this case
D.in no case