Answer the following question given this paragraph: 

The sunlight that reaches Earth is the planet’s most important source of energy. The energy in sunlight, called solar energy, is electromagnetic energy. This is a form of energy that travels through space in electric and magnetic waves. Solar energy can be used to heat homes and produce electricity in solar cells like those on the roof seen in the Figure below . Sunny areas receive plenty of sunlight to generate electricity, but solar energy may not be practical in areas that are often cloudy.


Q: What is the most important source of energy on earth?

 Choices:

- the earth's core

- water

- moon

- sun

A:
sun
