二次电气图是用于反映二次系统（）等的一种电气工程图。
A.工作原理
B.组成
C.连接关系
D.电器设备安装位置
参考答案：A, B, C
Questions 21 to 23 are based on the following news. At the end of the news item, you will be given 15 seconds to answer the questions. Now listen to the news
How long has Burma’s military been in power
A．For more than 30 years.
B．For more than 20 years.
C．For more than 50 years.
D．For more than 40 years.
保护层材料应符合哪些要求？
