The correct answer is - b. occupies Central and Southern Africa.
The Sahara desert is part of the hot deserts, mainly found in the Southern Hemisphere, and in close proximity to the Equator on both hemispheres. It is the largest desert in the world.
Sahara is occupying most of the northern part of the African continent, stretching between the plateaus in Central Africa and the Mediterranean coast, and from the Atlantic Ocean to the Red Sea.
