How does cutting down trees for firewood contribute to desertification in the sahel

Removal of wood - in developing countries, people use wood for cooking. As the population in desert areas increases, there is a greater need for fuel wood. When the land is cleared of trees, the roots of the trees no longer hold the soil together so it is more vulnerable to soil erosion .

Ibelieve that a would be the best answer.

Magma is outside the volcano  and lava is inside the volcano.