When an aeroplane is flying at a great height, the sky appears black to its passengers. Why?

• A. The dust particles and droplets of water present in the atmosphere absorb the light and do not follow it to reach the eyes of the passengers
• B. The atmosphere is very rare at great heights and so the scattering of lights is negligible
• C. The light is so polarized that no part of it is able to reach the eyes of the passengers
• D. None of the above