Explain causality in a system and what it implies about the impulse response.

• A. Causal system: output depends only on present and past inputs; h(t)=0 for t<0; h[n]=0 for n<0.
• B. Causal system: output depends on future inputs; h(t) nonzero for t<0.
• C. Causal system: impulse response is nonzero for all t.
• D. Causality is the same as stability.

Answer: (A)