速度和加速度的关系，下列说法中正确的是（ ）
A．速度大时，加速度一定大；速度小时，加速度一定小
B．速度的方向就是加速度的方向
C．速度改变量大，加速度一定很大
D．加速度为零时，速度不一定为零
A、物体的加速度等于物体的速度的变化率，与物体速度的大小无关．故A错误；
B、速度的方向与加速度的方向无直接关系，速度方向为运动方向，加速度方向是物体合力方向，故B错误
C、速度变化量大，即△v大，由加速度公式a=
，时间不一定，则加速度不一定大．故C错误．△v △t
D、加速度为零时，速度不一定为零，例如匀速直线运动，故D正确
故选D．
| 阅读理解。 根据短文内容 ，从短文后的选项中选出能填入空白处的最佳答案，选项中有两项为 多余选项。 | |
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