The black-bellied seedcracker is a species of bird found in central Africa. They live in various habitats where individuals eat either hard, large seeds or small, soft seeds. Individuals with thick, shorter beaks can eat the harder seeds. Individuals with thin, longer beaks can eat softer seeds. Individuals with beaks of intermediate thickness and length cannot really eat either type of seed very well. If you measured beak width and length in populations of black-bellied seedcrackers, what type of selection would you expect to find?

a. directional selection
b. disruptive selection
c. natural selection
d. stabilizing selection