题目

We're going to stay in Beijing for ______. A．a year and two       B．a year or two           C．a and two years     D．a or two years 答案：B质点做直线运动的v-t图像如图所示，规定向右为正方向，则该质点在前8s内平均速度的大小和方向分别为（ ）A．0．25m/s，向右 B．0．25m/s，向左C．1m/s，向右 D．1m/s，向左