题目内容

—Is Tom still not back?— No. By next year he _____ from home for three years.

A. will leave
B. will have been away
C. leaves
D. has been away

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The boy was caught cheating in the exam and _____by his headteacher at the moment.

A. was questioned
B. has questioned
C. is being questioned
D. has been questioning

I/O区的寄存器不能直接与PLC外部的输入、输出端子传递信息。

A. 对
B. 错

继电器、电磁阀和指示器件都可以做PLC的输出元件。

A. 对
B. 错

下列选项不是PLC的性能指标()。

A. I/O总点数
B. 程序存储器容量
C. 扫描速度
D. 自动控制