Why Does the Sun Look Flattened near the Horizon

Why does the Sun look flattened near the horizon?

A) The Sun's light is reflected off the horizon, making the Sun appear compressed.
B) Earth's dense atmosphere compresses the gaseous Sun.
C) The larger refraction near the horizon lifts the lower edge of the Sun more than the upper edge and makes the Sun look flattened.
D) The Sun is cooler on the horizon, so it looks flattened.