Decomposition adds silt to soil. Decomposition adds water to soil. Decomposition adds oxygen to soil. Decomposition adds nutrients to soil.
I gave my students this multiple choice question: Which of the following statements best explains how the decomposition of plant and animal matter helps to form rich soils?

Only one answer is correct among these 4 choices:
- Decomposition adds silt to soil.
- Decomposition adds water to soil.
- Decomposition adds oxygen to soil.
- Decomposition adds nutrients to soil.

Could you tell me which one is correct?

Decomposition adds nutrients to soil.