Mary is doing comparative anatomy as she is looking at the differences and similarities in the structures of distinct species.
What is comparative anatomy?
It is the study of the similarities and differences in the anatomy of distinct species. It is closely associated with phylogeny evolution and evolutionary biology. In this, the comparative study of the body composition of distinct species of animals is done in order to comprehend the adaptive variations they have gone through in the course of evolution.
Comparative anatomy has assisted in the classification of animals, and has provided proof of common descent. Therefore, in the given case, Mary is performing comparative anatomy by studying leg bones of different mammals.
Thus, the correct answer is option C.
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