电力系统中出现的内部过电压基本可以分为（）和（）两大类。
参考答案：稳态过电压;操作过电压
However busy we are, we need to take exercise. Not only___________us keep healthy, it also stops us getting fat.
A．it helps
B．helps it
C．it does help
D．does it help
节流装置有哪几条选择原则？
