Disruptive Selection Maintains a Bimodal Distribution of Bill Size in the West

Multiple Choice

Disruptive selection maintains a bimodal distribution of bill size in the West African seedcracker because

A) bills of intermediate shapes are difficult to form.
B) the birds' two major food sources differ markedly in size and hardness.
C) males use their large bills in displays.
D) migrants introduce different bill sizes into the population each year.
E) older birds need larger bills than younger birds.