The Pin/thrum Flower Polymorphism in Primroses

The pin/thrum flower polymorphism in primroses

A) is an example of nonrandom mating.
B) ensures that pollination occurs between individuals of the same genotype.
C) alters allele frequencies.
D) exists because pollen grains from pin and thrum flowers are deposited on the same parts of the body of insects that visit the flowers.
E) is a form of self-fertilization.