You are presented with the question "What decomposes in soil?" and the following answer choices: 
- swamp vegetation
 - roundworms
 - Echinoids
 - tunicates
 - Earthworms
 - some invertebrates
 - most cephalopods
 - Plant and animals

Now knowing that decomposition increases amount of organic matter in soil and organic matter is the plant and animal residue in the soil at various stages of decomposition, choose the best answer.


 

        Plant and animals 