Control Systems
The open loop transfer function of a unity feedback control system is given by G(s) = k/s(s+1). If gain k is increased to infinity, then damping ratio will tend to become

 unity
 zero
 infinite
 0.707

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

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