Answer the following question given this paragraph: 

Air temperature in the stratosphere layer increases with altitude. Why? The stratosphere gets most of its heat from the Sun. Therefore, it’s warmer closer to the Sun. The air at the bottom of the stratosphere is cold. The cold air is dense, so it doesn’t rise. As a result, there is little mixing of air in this layer.


Q: Where does the stratosphere get most of its heat?

 Choices:

- time

- earth

- volcanoes

- sun

A:
sun
