Which of the following pairs represents homologous organs?

Homologous organs are those that share a common ancestry, even if they have different functions in the organisms where they are found. The pectoral fins of fish and the forelimbs of horses are a classic example of homologous structures. Both belong to vertebrates and, during embryonic development, exhibit similar structural features despite being adapted for different purposes—swimming in the case of fish and running in the case of horses. This evolutionary relationship emphasizes the shared common descent, highlighting how different environmental pressures can lead to adaptations that serve distinct functional needs.

The other pairs mentioned do not represent homologous organs. The wings of insects and wings of birds, for instance, are examples of analogous structures, which arise independently in different evolutionary lineages. Similarly, the flippers of whales and fins of fish are adaptations to aquatic life but are not derived from a common ancestral structure, hence are not homologous. Lastly, while the ears of rabbits and humans both serve the function of hearing, they have evolved independently in response to different evolutionary pressures, making them more akin to analogous structures rather than homologous ones.