用所给词的适当形式填空

1. There ______ (be) a picture on the wall.

2. Are there ______(some) teachers in the classroom?

3. There ______(be) two pencils and a pen on the desk.

4. In the classroom,  there ______ (be) ten students and a teacher.

5. There aren't any ______ (apple) in the box.

单相桥式整流电流电路输入电压为8V，其输出电压为（）。

A.3.2V

B.3.6V

C.7.2V

D.8V