What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?

(N/A) Homologous structures are those organs or body parts that share a common basic structural design and developmental origin but perform different functions in different organisms.
Example: The forelimbs of humans,whales,bats,and cheetahs have the same basic skeletal structure (humerus,radius,ulna,carpals,metacarpals,and phalanges) but are adapted for different functions like grasping,swimming,flying,and running,respectively.
Yes,it is necessary that homologous structures have a common ancestor. This phenomenon is known as divergent evolution,where structures evolved from a common ancestral form and were modified over time to suit different environmental needs.