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单选题
840、Extend and retract the actuator through three full cycles.
A
Do nothing to the actuator after three complete cycles.
B
After three full cycles, extend and retract the actuator.
C
You should extend and retract the actuator through three complete cycles.
答案解析
正确答案：C
解析：
解析:注释: Extend 延伸,伸出; retract 缩回,r 收起。through 通过。
相关知识点：
执行动器三全循环伸缩
