讲解当前题目---**Question Stem:** 【例 3】 如图所示为一物体做匀变速直线运动的速度—时间图线，根据图线做出的以下几个判断，正确的是 **Options:** A. 物体始终沿正方向运动 B. 物体先沿负方向运动，在 t=2s 后开始沿正方向运动 C. 在 t=2s 前，物体位于出发点负方向上，在 t=2s 后，物体位于出发点正方向上 D. 前 4s 内，当 t=2s 时，物体距出发点最远 **Chart/Diagram Description:** * **Type:** Velocity-time (v-t) graph. * **X-axis:** Represents time, labeled "t/s" (time in seconds). Scale shows marked points at 0, 2, and 4. * **Y-axis:** Represents velocity, labeled "v/(m·s⁻¹)" (velocity in meters per second). Scale shows marked points at -20, 0, and 20. * **Graph Line:** A straight line segment representing the motion. * It starts at t=0s with a velocity of -20 m/s (point (0, -20)). * It crosses the t-axis (v=0) at t=2s (point (2, 0)). * It reaches a velocity of 20 m/s at t=4s (point (4, 20)). * **Annotations:** Dashed lines extend from the point (4, 20) to both the t-axis and the v-axis to highlight these values. **Answer:** 答案: BD