In a comparison of birds and mammals, the condition of having four limbs is .
a. a shared ancestral character.
b. a character useful for distinguishing birds from mammals.
c. a character useful for sorting bird species.
d. a shared derived character.
e. an example of analogy rather than homolog

a. A shared ancestral character.

Explanation:

The condition of birds and mammals having four limbs is a shared ancestral character because the structure of the limbs are similar in both the cases.

The forelimbs of the bird are modified into wings to aid flying.The hind limbs are modified into feel and claws.

These are homologous structures to the hands and feet in mammals.

That means they have a common origin, and hence are shared ancestral character.

straight or amphibians are homeothermic to thermal