完形填空题

     My family members like to use computers. We live in China. My aunt1in Australia. My mother and my aunt often2e-mails to each other. Sometimes3chat(聊天) online.

     My father is a4in a middle school. He often searches for5for his lessons6the Internet.

     My brother and I like to7computer games. I like to play Counter Strike, but he likes to play Seer(赛尔号). My8don't like us to play them too long. They say that playing computer games too long is bad for our9and study. We both like music, too. So sometimes we10music on the computer.

一位同学为探月宇航员设计了如下实验：在距月球表面高h处以初速度v_o水平抛出一个物体，然后测量该平抛物体的水平位移为x，通过查阅资料知道月球的半径为R，引力常量为G，若物体只受月球引力的作用，求：

在竖直向上的匀强电场中，一根不可伸长的绝缘细绳的一端系着一个带电小球，另一端固定于O点，小球在竖直平面内做匀速圆周运动，最高点为a，最低点为b，不计空气阻力，则（   ）