题目内容

PLC的辅助继电器相当于传统继电器-接触器控制系统的中间继电器，其编号由M和（）（八进制/十进制）数组成，如M10、M68等。

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M8002是初始化脉冲特殊辅助继电器，它仅在PLC运行开始的第一个扫描周期（）（断开/接通 )。

M8013是产生周期为（）（1s/1min）时钟脉冲的特殊辅助继电器。

Miss Smith's assistant enjoys ______ for her although she treats him very strictly.

A. work
B. working
C. to work
D. Worked

Have you ever heard about the meeting ______ tomorrow?

A. held
B. to be held
C. being held
D. holding