A particular environmental change causes the deaths of 25 individuals in a herd of 100 wild horses, and it kills 50 individuals in a herd of 200 horses. In this case, the growth of a wild horse population is most likely limited by __________. (Assume that the two herds are found in territories of equal size.)

• A. a density-dependent factor
• B. food supply
• C. a predator
• D. the presence of another species that uses the same food resource
• E. a density-independent factor