emission of light by land and water surfaces reflection of light from land and water surfaces absorption of light by matter in the atmosphere scattering of light by matter in the atmosphere
I gave my students this multiple choice question: What causes the blue color of the sky?

Only one answer is correct among these 4 choices:
- emission of light by land and water surfaces
- reflection of light from land and water surfaces
- absorption of light by matter in the atmosphere
- scattering of light by matter in the atmosphere

Could you tell me which one is correct?

scattering of light by matter in the atmosphere