Fact 1: Freezing means changing from a liquid into a solid by reducing heat energy.

Fact 2: Solid ice is melted into liquid water.

Given the two facts above, answer the question "How does water turn to ice?" with the following options: 
- Adding air
 - The bending of a ray of light
 - Warm air moving into cold air
 - Increasing heat energy
 - It used to be covered by water
 - evaporation
 - Adding salt
 - Reducing heat energy


 

        Reducing heat energy 