Fact 1: Earthworm burrows help aerate soil, which is also good for plants.

Fact 2: Insects and earthworms are very important in mixing and aerating the soil.

Given the two facts above, answer the question "What do earthworms mix?" with the following options: 
- roots
 - rocks
 - soil
 - nitrogen
 - ocean
 - Carbon
 - Crops
 - well


 

   soil      