题目内容

下列关于S7200PLC中，定时器指令的说法正确的是（）

A. 接通延时定时器可用于某些设备按一定时间顺序，顺序启动时
B. 断开延时定时器可用于某些设备按一定时间顺序，顺序停止时
C. 保持性接通延时定时器可用于累计某故障发生的时间
D. 可以用定时器指令产生任意频率的脉冲

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