Final answer:Whales have a femur and pelvis because they are descended from land-dwelling ancestors. Through vestigial evolution, these limbs became reduced over time, leading to the vestigial structures present in modern whales, which also indicate a common ancestry with other vertebrates. The correct option is C.Explanation:Whales possess a femur and a pelvis because they descended from organisms that walked on land. Modern whales evolved from four-legged land mammals and later adapted to life in the water, which rendered their hind limbs unnecessary for their aquatic lifestyle.As a result, these limbs became reduced over time through a process of vestigial evolution, leaving behind remnants of the pelvic bones and the undeveloped hind legs, which are still present as vestigial structures in today's whales. The presence of a femur and a pelvis in whales also highlights the concept of homologous structures, which are anatomical features that are similar in different species due to shared ancestry.This similarity suggests that these species, including whales, birds, and humans, share a common ancestor. Fossil records of ancient cetaceans, such as Pakicetus and Rodhocetus, provide evidence of the transition from land to water, showing traits of both land mammals and modern whales.Therefore, the correct option is C....

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