runoff of water. erosion of sand dunes. compaction of rock layers. decomposition of plants and animals.
I gave my students this multiple choice question: Soil texture is improved by

Only one answer is correct among these 4 choices:
- runoff of water.
- erosion of sand dunes.
- compaction of rock layers.
- decomposition of plants and animals.

Could you tell me which one is correct?

decomposition of plants and animals.