题目内容

8. It’s been a long time since I ___. How are you?

A) had last seen you
B) saw you last
C) have least seen you
D) last was seeing you

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9. We ___ on it for several hours but we have not yet reached any conclusion.

A) work
B) are working
C) have been working
D) have been worked

10. He said that he ___ for Shanghai the next day.

A) will leave
B) has left
C) would leave
D) had left

在电动机的继电器接触器控制电路中，自锁环节的功能是()。

A. 具有零压保护
B. 保证电动机起动后持续运行
C. 兼有点动功能
D. 具有保护功能

某一控制电路，只有在按下按钮时，电动机才能起动运转，松开按钮时，电动机立即停止运转，这种控制方式称为( )。