Most of the African continent is on a high "plateau". Although it is true that African contains the largest desert in the world, the desert itself is not physically "high" in the same sense.
The Mongols treated the non-muslim subjects most fairly, while the Ottomans treated them the least fairly.
The Mongols were religiously tolerant because they conquered and rule through manpower rather than religion. The Ottomans were the least fair to non-muslims. It is close between the Umayyads and the Ottomans, but the only difference is the amount of discrimination (per se) held against non-muslims. While the Umayyads only had the jizya (tax paid if you were non-muslim), the Ottomans had distinctive restrictions on non-muslims. They had dress codes according to their religion and could only reside in neighborhoods who's residents were of the same religion (under the Ottomans).
The correct answer would be D. footnote
