Final answer:
A graph showing a very narrow, very tall peak at the natural frequency suggests that the system is resonant, which occurs when a system is driven at its natural frequency and exhibits large oscillations due to minimal damping (C).
Step-by-step explanation:
If you observe a graph of amplitude vs frequency and at the natural frequency you see a very narrow, very tall peak, the system is probably resonant. Resonance occurs when a periodic force drives a harmonic oscillator at its natural frequency, resulting in a significant increase in the amplitude of oscillation. This condition implies that there is little damping in the system, and it can sustain large oscillations at the natural frequency.
According to the information provided, less damping leads to higher amplitudes near the resonant frequency. On the other hand, an underdamped system will oscillate through the equilibrium position, while an overdamped system will move more slowly toward equilibrium. A critically damped system returns to equilibrium as quickly as possible without overshooting more than once.