What evidence did Chapman and Chapman (2000) use to conclude that competition limits group size in the primates they studied?

A) They found a positive correlation between group size and the density of food trees.
B) They observed a decline in group size with a natural decline in food availability.
C) They observed an increase in group size with the experimental addition of food.
D) They observed an increase in fitness of individuals with a decline in group size.
E) They observed an increase in group size with an experimental reduction in competitors.