Fact 1: Changes in the pH of soil can cause plants to die.

Fact 2: Compost balances the pH of soil.

Given the two facts above, answer the question "What balances the soil?" with the following options: 
- rivers
 - salinity
 - nutrients
 - heat
 - compost
 - Earthworms
 - roundworms
 - Annelids


 

     compost    