They eliminate matter by taking nitrogen from the ecosystem. They eliminate matter by taking phosphorus from the ecosystem. They cycle matter by returning carbon and other matter to the ecosystem. They cycle matter by returning oxygen and other matter to the ecosystem.
I gave my students this multiple choice question: What is a primary role of decomposers in an ecosystem?

Only one answer is correct among these 4 choices:
- They eliminate matter by taking nitrogen from the ecosystem.
- They eliminate matter by taking phosphorus from the ecosystem.
- They cycle matter by returning carbon and other matter to the ecosystem.
- They cycle matter by returning oxygen and other matter to the ecosystem.

Could you tell me which one is correct?

They cycle matter by returning carbon and other matter to the ecosystem.