The correct answer is [A] Atmospheric refraction of starlight.

[A] Atmospheric refraction of starlight is the main cause of the twinkling of stars. When light from a star enters the Earth’s atmosphere, it is bent or refracted by different layers of air at different temperatures and densities.

This causes the light to take different paths to our eyes, making it appear as if the star is twinkling or dancing.

[B] Dispersion of starlight is not a cause of the twinkling of stars. Dispersion is the phenomenon by which light is separated into its component colors, such as when light passes through a prism and creates a rainbow.

[C] Scattering of starlight is also not a cause of the twinkling of stars. Scattering is the phenomenon by which light is redirected in many different directions by small particles in the atmosphere, such as dust or water droplets. This causes the sky to appear blue during the day and causes the phenomenon of the blue light scattering around the sun during sunset and sunrise

[D] None of the above is not a correct answer, as the twinkling of stars is caused by the atmospheric refraction of starlight.

The correct answer is [A] Atmospheric refraction of starlight.