今年2月27日江苏有一面包车上掉下一小孩，接着小孩追赶一段距离后无法追上而停止下来．小孩静止时，面包车正以速度v=10m/s保持匀速直线运动且与小孩的距离L=20m，此时，小孩身后x=4m处有一轿车发现状况后以初速度v₀=4m/s立即做匀减速直线运动，到达小孩处速度恰好为零，再经△t=6s，轿车司机把小孩接上车后立即从静止开始以加速度a=2.5m/s²做匀加速直线运动追赶前方匀速运动的面包车，若轿车的行驶速度不能超过v_m=54km/h．求：

    My name is Bob.Tomorrow is Saturday.We have no classes.My parents aren't going to work，but we are going to be very busy tomorrow.My mother is going to buy something.My father is going to visit my aunt and uncle.I'm going to the bookstore by bus.Then I'm going to buy a dictionary.Tomorrow evening we are going to visit my grandparents and have a big dinner.After that we are going to the cinema.

如图是有关绿色开花植物的形态结构示意图，请据图回答：

按照气体分子热运动的理论，气体对器壁的压力是由于分子对器壁的____而产生的．一定质量的气体，在温度不变时，气体的体积越小，分子数越密集，一定时间内撞到单位面积器壁的分子数就____，气体的压强就____．