A:a、b同号
B:a、b异号且负数的绝对值较大
C:a、b异号且正数的绝对值较大
D:以上均有可能
The______is a piece of metal,plastic or bone with teeth,used for tidying and arranging the hair.
—Is it ________ one on the chair near the door?
一列简谐横波沿x轴正方向传播,波速v=4m/s,已知坐标原点(x=0)处质点的振动图象如图所示,在下列4幅图中能够正确表示t=0.25s时波形的图是( )