If Each Breeding Pair of Elephants Produces 6 Offspring During

If each breeding pair of elephants produces 6 offspring during a 90-year life span, in 750 years, a single pair of elephants will have given rise to a population of 15 million elephants. Yet elephants have not overrun the planet. WHY?

A) Elephants have a niche that expands with the population.
B) Elephants produce more offspring than will survive to maturity.
C) Most elephants are kept in captivity (circus & zoo) and not allowed to reproduce.
D) Individual elephants in a population exhibit no variation, reducing their reproductive success.