Question

the forearms of a human, a horse, and a bat are shown in the diagram.
how do these structures provide evidence for common ancestry?
the mammals do not share a common ancestor. the differences in forearm functions have evolved from independent lineages, but appear to have similar bone structures.
the mammals share a common ancestor. the differences in forearm functions have evolved from the same ancestral bone structure.
the mammals share a common ancestor. the forearms each share a similar ancestral function, even though they have evolved to form different bone structures.
the mammals do not share a common ancestor. the differences in forearm bone structures have evolved from independent lineages, but share similarities in function.

Explanation:

Homologous structures, like the forearms of human, horse, and bat, have a common ancestral origin. Despite different functions (e.g., grasping, running, flying), their similar bone - structure (derived from the same ancestral bone structure) indicates common ancestry.

Answer:

The mammals share a common ancestor. The differences in forearm functions have evolved from the same ancestral bone structure.