甲烷制冷压缩机的等级维护包括（）。
A．日常维护
B．一级保养
C．二级保养
D．三级保养
参考答案：A, B, C, D
It is believed that the tight employment market has forced job seekers to_______whatever work is available.
A．take up
B．take down
C．take off
D．take on
RCS-985保护中发电机纵差保护主要功能？
