Explanation:

Black soil, known for its high clay content, excellent moisture retention capacity, and richness in nutrients like lime, iron, and magnesium, is ideally suited for cotton cultivation. This soil type is also popularly known as Regur soil. Therefore, option D is correct. Option A, Khadar, refers to new alluvial soil found in floodplains, which is fertile but distinct from black soil. Option B, Bangar, refers to old alluvial soil found above floodplains, also distinct. Option C, Kankar, refers to calcareous concretions or nodules found in some soils, not a type of soil itself. Thus, A, B, and C are incorrect terms for black soil.