Tropical regions show greatest level of species richness because: $\newline$ A. Tropical latitudes have remained relatively undisturbed for millions of years, hence more time was available for species diversification. $\newline$ B. Tropical environments are more seasonal. $\newline$ C. More solar energy is available in tropics. $\newline$ D. Constant environments promote niche specialization. $\newline$ E. Tropical environments are constant and predictable.