Control Systems
Negative feedback in a closed loop control system

 improves disturbance rejection.
 reduces sensitivity to parameter variation.
All of these
 reduces gain.

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Control Systems
A cascade of three linear time invariant systems is causal and unstable. From this we conclude that

 at least one system is unstable and at least one system is causal.
 the majority are unstable and the majority are causal.
 at least one system is causal and all systems are unstable.
 each system in the cascade is individually caused and unstable.

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