Option A (Tropical Regions) is correct because the textbook explicitly states that 'Biodiversity is not found evenly on the earth. It is consistently richer in the tropics.' Additionally, the context mentions that countries situated in the tropical region possess a large number of the world's species diversity and are called mega diversity centres. In contrast, as one approaches the polar regions, one finds larger populations of fewer species, indicating lower biodiversity in polar and temperate regions compared to tropical regions.