Why Do Tropical Communities Tend to Have Greater Species Diversity

Why do tropical communities tend to have greater species diversity than temperate or polar communities?

A) They are less likely to be affected by human disturbance.
B) There are fewer parasites to negatively affect the health of tropical communities.
C) Tropical communities are low in altitude, whereas temperate and polar communities are high in altitude.
D) Tropical communities are generally older than temperate and polar communities.
E) More competitive dominant species have evolved in temperate and polar communities.