Fact 1: Energy enters ecosystems in the form of sunlight or chemical compounds.

Fact 2: Energy is a basic necessity of an ecosystem.

Given the two facts above, answer the question "the basic necessity of an ecosystem enters in the form of what?" with the following options: 
- heat
 - recycling
 - trees
 - food
 - sunlight
 - adding heat
 - movement
 - root growth


 

     sunlight    