直流电源跟一个线圈连接成闭合回路，线圈的上方和右侧各有一个可以自由转动的小磁针，它们静止时如图所示，则下列判断正确的是

A．小磁针的c端为N极，电源的a端为正极

B．小磁针的c端为N极，电源的a端为负极

C．小磁针的d端为N极，电源的a端为正极

D．小磁针的d端为N极，电源的a端为负极

根据句意和汉语提示，填写恰当的短语完成下列句子。

1. I hope you can come back___________ (尽快地).

2. All the teachers ____________(乐意帮助) students to solve their problems.

3. We should ___________(坚持) our dreams and try to achieve them.

4. ____________(数以千计的) students were surveyed about their favorite foods.

5. My sister _____________(梦想) becoming a singer. She likes singing very much.