汽车在平直的公路上以20m/s 的速度行驶,当汽车以4m/s2的加速度刹车时,刹车2s内与刹车6s内的位移之比为( )
A:2:3
B:3:4
C:3:1
D:16:25
—I am really struck by your spoken English. You speak so fluently. Have you been abroad?
—Yes. I ______ in London for two years.
如图所示,弹簧振子在BC振动,O为平衡位置,BO=OC=5cm,若振子从B到C的运动时间是1s,则下列说法中正确的是( )