You are presented with the question "what makes soil stable?" and the following answer choices: 
- weather
 - heat
 - magma
 - rain
 - streams
 - water
 - trees
 - crust

Now knowing that the looseness of soil has a positive impact on a plant 's roots' growth in that soil and tree roots stabilize the soil and prevent soil erosion, choose the best answer.


 

       trees  