Answer:
Frequency
Explanation:
[tex]\dfrac{\text{Number of wavelengths}}{\text{Time }} = \textbf{frequency}[/tex]
If you are at the beach, you may see six waves go past you in half a minute.
An hour later, you see only three waves in the same time.
You would say that the frequency of the waves has decreased.
A is wrong. Wavelength is the distance between one wave and the next.
B is wrong. Speed is a measure of how fast the waves are travelling.
D is wrong. Amplitude is the height of a wave from its resting position (half the distance from a peak to a trough).
