It's often Linux since Linux is free, but it could be Windows.
Answer:
Sensing elements.
Explanation:
Sensing elements are the device which connect channels feedback and return it to the control system input. There are many sensors used for feedback control such as Tachometer, Encoders, Accelerometers and rate gyroscopes.
Social Engineering.
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That if something happens such as some one gets cancer you can pay for it or if you lose your job you can still have time to react and get a new job
