On a sunny clear day, the sky seems to be bluer directly overhead than it does toward the horizon. Which of the following is the reason?

W) Light from the Sun undergoes more scattering with distance X) The atmosphere has higher density at the zenith versus closer to the Earth's surface Y) There is more oxygen in the air closer to the Earth's surface than high in the atmosphere Z) The upper atmosphere is colder than the Earth's surface
W) LIGHT FROM THE SUN UNDERGOES MORE SCATTERING WITH DISTANCE