The country that is mainly covered by the Kalahari Desert in the Southern subregion of sub-Saharan Africa is Botswana (Option C). To find this answer, you can either have prior knowledge about the Kalahari Desert and its location, or you can conduct a quick online search using search engines like Google. By searching for "Kalahari Desert in Southern sub-Saharan Africa," you will find that Botswana is the country primarily covered by this desert.