Answer: a. Stabilizing selection
Stabilizing selection is the type of natural selection in which intermediate traits in an organism is selected by the nature and those with extreme characteristics or trait does not get any benefit. The organisms with intermediate characteristics are suitable for the environment and hence, selected by the nature. These organisms exhibit limited number of adaptations. Hence, they experience limited evolutionary changes.
Stabilization selection is a selection pressure which is responsible for the limited evolutionary changes experienced by alligators and other crocodilians.