题目

（9分）A、B、C三地彼此间的距离均为 a，如图所示 物体以每秒走完距离a的速度从A点出发，沿折线经B、C点又回到A点，试分析说明从运动开始经1s、2s、3s，物体的位移大小和路程各为多少？ 答案：a， a； a，2a；零，3a注意：位移与路程的区别，前者是矢量，后者是标量。这是学生容易混淆的两个概念。All these donations must be delivered immediately________in time for Christmas.A. so as to have received B. in order to be receivedC. so as to receive D. in order to be receiving