For what reason does Frank ask for sick leave?[音频]
A. He has caught a cold.
B. He didn't sleep well last night.
C. He has got a headache.
Which of the following is true about Frank’s mother?
A. She works in a hospital.
B. She is in hospital because of a heart attack.
C. She has spent a week with Frank since she was ill.
What does Bill ask Frank to do before he takes his leave?
Ask Lisa to help with his project.
B. Present a detailed progress report.
C. See his mother immediately.
1、与继电控制及一般的计算机控制相比较，可编程控制器有什么特点？
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