磁场中某一点的磁感应强度与媒介质的磁导率的比值叫做（）。
A、磁场强度
B、磁导率
C、磁力线
D、磁通量
参考答案：A
读句子，选答语。
1. Are they horses?[ ]
A. Yes, they are.
B. No, they are.
2. What are they? [ ]
A. They are donkey.
B. They are donkeys.
3. How many cows do you have?[ ]
A. One hundred.
B. They are fat.
4. Are those horses? [ ]
A. Yes, those are.
B. Yes, they are.
A．若磁场正在增强，则电场能正在减少，电容器上极板带正电
B．若磁场正在减弱，则电场能正在增强，电容器上极板带正电
C．振荡电流的变化周期为：2π
D．电场能量的变化周期为：π
