Answer:
The correct answer is option 2. Common ancestry.
Explanation:
The homologous structure is the structure that has a similar anatomical structure or underlying skeleton and can perform a different function in different organisms.
Homologous structures are similar in different organisms because they diverge from a common ancestor. All organisms that have homologous structures are considered to have a common ancestry. for example, human arm, dogs forearm, bat's wing all have a similar skeleton structure
Thus, the correct answer is option 2. Common ancestry.