Here's a problem to solve: In many parts of the world, land that is too dry for farming is used for grazing livestock. Overgrazing of these lands destroys the native plants and breaks down the natural soil covering. How does overgrazing result in desertification?

Among the 4 following options, which is the correct answer?

- A: by increasing the rate at which topsoil is eroded
 
- B: by allowing non-native species to colonize the land
 
- C: by reducing the food available to livestock
 
- D: by causing the land to absorb rainfall more quickly
 