Final answer:
Homologous structures are similarities in organisms due to inheritance from a common ancestor, even if their functions differ. The limbs of mammals, such as the wings of bats and the arms of humans, are homologous. The correct answer is b) Structures with different functions but a common evolutionary origin.
Step-by-step explanation:
Homologous structures are features in different organisms that are similar because they were inherited from a common ancestor. Homologous structures may serve different functions in those organisms. An example of a homologous structure is the skeleton of the forelimbs in mammals, such as bats, whales, and humans, which have been adapted to different activities like flying, swimming, and manipulating objects, respectively. This adaptation is evident despite their different functions, as they share an underlying similarity in bone structure.
The correct answer to the question is b) Structures with different functions but a common evolutionary origin. Unlike homologous structures, analogous structures have a similar function but do not share a common ancestor; they result from convergent evolution. An example of analogous structures would be the wings of birds and butterflies, which serve the purpose of flight but evolved independently in these very different organisms.