What is an example of homologous structures?

Option D is correct.
The wings of a bird and those of an insect is least likely to be homologous.

Homology in biology is the similarities of structures, physiology and development of different species of organisms from a common evolutionary ancestor.

The wings of a bat and arm of human are similar, the upper forelimbs of humans and bat have similar skeletal structure.

The hemoglobin of a baboon and that of a gorilla is also similar. DNA sequence are similar in both baboons and gorillas.

The mitochondria in plants and animals have similar organelles. The brain of a cat and a dog is also similar.