Food Chains Are Usually Short

Multiple Choice

Food chains are usually short. Reasons for this are thought to be

A) the energy available at each level.
B) populations of organisms in a food web are in stable equilibrium, which is maintained by short chains.
C) there is a hierarchy in which species fed on those below and are eaten by those in levels above it, and so is limited by the tropic levels.
D) the relatively few organisms in any ecosystem.
E) Generally the reasons are unknown.