Answer: The correct answer is " because the wave speed remains constant".
Explanation:
The expression of the wavelength in terms of the frequency is as follows;
Here, c is the speed of the light, f is the frequency of the wave and is the wavelength of the wave.
The wavelength of the wave is inversely proportional to the frequency of the wave as the speed of the wave remains constant.
If the wavelength of the wave decreases then the frequency of the wave increases.
Therefore, the frequency of a wave increases as the wavelength decreases because the wave speed remains constant.
The correct option is (A).