The correct answer is - C. desertification.
The changes in climate that contributed to big droughts in the past few decades in Africa, as well as the irresponsible actions in the matter of water usage, like the leaching, led to desertification in areas where the desert was not present till recently. The Sahara Desert has been slowly moving its southern border towards south, and areas that were once inhabited by people, or where wildlife was roaming, are now turned into deserts, and this causes lots of problems in economic and social aspects, as well as destroying the environment and endangering lots of wild species of animals and plants.
