Discussion
An amplifier oscillates at high frequency only when a long loudspeaker cable is fitted. Why?
Answer: B
A long cable presents tens of nanofarads, and that capacitance works against the output impedance to add a pole inside the feedback loop, eating the phase margin. Resistance and inductance affect damping and response rather than stability, and interference would appear as noise rather than oscillation. The standard remedy is a small series inductor at the output, keeping the cable's pole outside the loop - which is why one is fitted in almost every commercial amplifier.
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