题目

一个物体自距地面高为H的位置处自由下落（不计空气阻力），当它的速度到达着地速度的一半时，它下落的高度为 ( ) A . H/2 B . H/4 C . 3H/4 D . H/8 答案：B—Tom，you’ve got an A in the final English exam.Congratulations!—Thanks.But I never thought the result came out so fast.The papers________when I left the teacher’s office just now.A．had been marked B．were still being marked C．are still marking D．had been marking