Question

what is resonance?
multiple choice
essentially the same thing as a strong echo.
a sympathetic vibration that randomly occurs.
the matching of an external force with a natural frequency.
a harmonic reverberation that occurs at certain frequencies.

Explanation:

Resonance is a phenomenon where an external force or vibration matches the natural frequency of a system, causing a significant increase in amplitude. An echo is a reflection of sound. Sympathetic vibration is related but resonance is not random. Harmonic reverberation is not the exact definition.

Answer:

The matching of an external force with a natural frequency.