15. Sarah is a biologist who is studying a species of crab. In the wild, crabs with larger

The answer is B. The fraction of crabs exhibiting large claws would rise. Crabs with larger pincers are likelier to survive and mate; this evolutionary advantage ensures that a majority of these crabs will successfully reproduce over generations and pass down this trait to their young. In contrast, smaller-clawed crabs lack this reproductive or survival benefit, which results in many of them either perishing prematurely or failing to reproduce, thus not transmitting this characteristic to their progeny. In the long term of several generations, the trait for larger claws will dominate, while that for small claws will diminish due to the increased adaptability of crabs with bigger claws. Consequently, we expect an increase in the proportion of crabs with larger pincers.