Why are there so few ecosystems with more than four levels of consumers?

• A. because biomass decreases by about 90% at each level moving up.
• B. because top consumers compete with and kill each other with increasing population size.
• C. because consumers at these highest levels typically form social groups that stop reproducing at high densities.
• D. because predators at the highest levels simply are not intelligent enough to hunt other top predators.