They make the soil clean. They keep disease out of the soil. They recycle nutrients into the soil. They remove extra water from the soil.
I gave my students this multiple choice question: Which best describes how earthworms improve soil as they eat dead plant material?

Only one answer is correct among these 4 choices:
- They make the soil clean.
- They keep disease out of the soil.
- They recycle nutrients into the soil.
- They remove extra water from the soil.

Could you tell me which one is correct?

They recycle nutrients into the soil.