题目

One day an old man was taking the train to his hometown. Suddenly one of his shoes fell onto the ground . but the train started, he couldn’t pick it up. The he took off the other and threw it near the falling shoe. A boy nearby asked him, “Why did you do that ?”  He answered with a smile. “If a poor man picks them up. He may get a pair of shoes.” (  ) 1.The old man was going to his hometown________ A  by bus  B  by train  C  on foot (  ) 2.How many shoes fell onto the ground  A  Only one  B  Two  C  A pair  (  ) 3.Why couldn’t the old man pick up the fal如图所示，一平行板电容器电容为C，极板间距为d，所带电量为Q，在两极板正中间固定一电量为q的点电荷，k为静电恒量，则上极板对该点电荷的电场力大小为（ ）A．B．C．D．