如图所示，O是AB的中点，a、b是AB连线上的两点，c、d是AB中垂线上的两点，Oa=Ob=Oc=Od．若在A、B两点分别放两个等量的正点电荷，取无穷远处为零电势点，则下列说法正确的是（　　）

A．a、b两点的场强相同

B．c、d两点的电势相等

C．将一个正电荷从a点移动到c点，电场力做功为零

D．将一个正电荷从a点移动到b点，电场力做功为零

根据句意，用所给单词正确形式完成句子。

1. He studies English by             (make) vocabulary lists.

2. You should pay more attention to your            (pronounce).

3. I'm too             (excite) to say anything.

4. Can you always understand             (speak) English?

5. I want some            (suggest) about learning English.

6. Reading more books is            (help) what to do today.

7. I can understand what they said             (complete).

8. Everyone wants to become a good language            (learn).

9. My grandfather enjoys            (watch) Beijing Opera.

10. He has a good             (memorize) for numbers.