Period from displacement-time graph

Steps:

• Displacement-time graph for a point on the string shows oscillation over time.
• Points X and Y mark identical positions in consecutive cycles.
• Horizontal axis is time, so distance between X and Y measures time interval.
• This interval is the time for one full cycle, defining the period.

Why C is correct:

• Period T is the time for one complete oscillation, directly given by the horizontal distance between repeating points on a d-t graph.

Why the others are wrong:

• A: Amplitude is maximum vertical displacement on the graph.
• B: Frequency is cycles per second (1/T), not a time distance.
• D: Wavelength is spatial distance between crests, measured on a position-time graph, not time axis.

Final answer: C