The graph below shows the size of the male and female in a large number of matings of an insect ...

The graph below shows the size of the male and female in a large number of matings of an insect species observed in nature.
 
  A separate study showed that large females produce more eggs than small females. What is a possible explanation for the observed pattern?
 
  a. Large males are more successful at defending access to large females.
  b. The samples were taken along an environmental gradient that influences the body size of both males and females.
  c. Females compete for high quality large males with larger females winning the competition.
  d. The copulatory organs form a tightly tuned lock and key system that does not allow for large size differences in the mating partners.
  e. All of the above.