Give an example of a characteristic being used to determine how close two species are on evolutionary terms?

Hint: Species is a basic unit of classification. The relative closeness of two species can be using a character called the homologous structures. Homologous organs are organs with the same origin and similar basic structure.

Complete answer: These are similar in different species, because of their inheritance from a common ancestor. For example, the limbs of the human, frog, lizard, and bird have a similar structure. Functions performed by all the limbs, mentioned above are different. All animals have carpals, metacarpals, radius, ulna, humerus, and phalanges in their forelimbs but have a varied function. Hearts of vertebrates like fishes, amphibians, reptiles, birds and mammals have a similar basic plan but they possess different degrees of specialization. Based on the habitat they live in, energy requirement varies thus the degree of complexity also varies. Another example of homologous organs is the thorn of bougainvillea and tendril of cucurbita. Both are axillary in position and both are axillary bud modifications but function of thorn is the protection and function of tendril is to provide support. As the internal structure is the same it shows the evolutionary relationship.

Additional points:
Divergent evolution is responsible for the evolution of homologous organs. According to some taxonomists, two species are morphologically distinct when they are reproductively isolated. Members of a particular species show a close resemblance to other species.

Note: Homologous organ varies from analogous organ. Analogous organs are defined as the organ of different animals that are having different structures but they perform the same function.
Examples: wings of the insect and wings of birds, the eye of octopus and eye of mammals. Convergent evolution is responsible for the formation of the analogous organ.