Fact 1: Soil is formed by rocks eroding.

Fact 2: Rivers erode the rocks they flow over.

Given the two facts above, answer the question "The movement of this body aids in the formation of soil." with the following options: 
- solar system
 - rain
 - streams
 - forces
 - body politic
 - human nature
 - river
 - wind


 

       river  