Which of the following factors can lead to desertification in the presence of natural drought? a. deforestation b. sustainable grazing c. underground mining d. all of the above (not b)

The answer is A. deforestation

Trees and another various type of vegetations played really important roles in absorbing water (through their pores/roots)
So, when deforestation happens, we cut down many of these trees and vegetation, which heavily reduced the absorption capability in that area,  which eventually cause desertification in the long run.