-----Good evening. Huangshan Hotel.

-----Good evening. ______________?

A．Do you still have a room for tonight

B．What would you like, please

C．Is there anything I can do for you

D．Who is that speaking, please

磁力线是描述磁场结构的一组曲线，磁力线的疏密程度，反映磁场中各点磁场的强弱。