The answer is A. This is because sunlight is composed of various wavelengths in the electromagnetic spectrum. In the visible light spectrum, red light has a higher frequency (lower wavelength) than blue light that has a lower frequency (higher wavelength). Therefore red light has higher energy than blue light hence able to penetrate more into the atmosphere before scattering, compared to blue light. At sunrise and sunset, due to the relative angle of the sun to the observer, the sun rays have to penetrate a thicker layer to the atmosphere before reaching the observer