There are a lot of______in our school. They work very hard.     [ ]

A. woman teachers        

B. women teachers   

C. woman teacher             

D. women teacher

一类负荷中的应急电源包括（）。

A、独立于正常电源的发电机组

B、供电网络中独立于正常电源的专用馈电线路

C、蓄电池组

D、正常电源之一