如图，A、B为两等量异号点电荷，dbe为中垂线，ab＝bc、be=db,则 ( ) 
A．a点与c点的电场强度相同 B．a点与c点的电势相同
C．a、b间电势差与b、c间电势差相同 D．在d点释放一电荷，它将在中垂线上d、e之间来回运动
AC
ac两点电场强度首先方向相同，由A指向B,又由于电场强度大小关于中轴线对称，所以A正确，沿着电场线方向电势减小，所以B错误。由A可得C正确。在d点放一电荷，所受力沿水平方向，所以D错误。
| 用方框中所给词的适当形式填空, 其中有两个词是多余的. | |
| |
| l. It's snowing hard outside. It's very __ __ now. 2. —How is it __ __ in your new school? —Not bad. 3. People like to swim in summer because it is too __ __. 4. The weather in Hainan is __ __ all year round, so people can grow rice three times a year there. 5. It gets __ __ when autumn (秋天) comes. |