Hi @zwa39, thanks for your question. Please note that this is a strengthen question. Specifically, you are being asked to strengthen the conclusion that "the fragile hind limbs [on this found whale fossil] are remnants of limbs that land-dwelling whales once had."
Notice that the stimulus states "if animals have a pelvis, we expect them to have hind limbs." Yet this whale fossil, which has a partial pelvis, had "very fragile hind limbs that could not have supported the animal's weight on land."
To connect the dots and strengthen the conclusion, we need to find an answer choice that explains how a fossil with only a partial pelvis and very fragile hind limbs is somehow still connected to the limbs that land-dwelling whales once had.
Answer choice (A) does exactly this: "Whale bones older than the fossilized hind limbs confirm that ancient whales had full pelvises."
If this is true, then the fossil found is just later down the evolutionary line from land-dwelling whales. Put differently, land-dwelling whales evolved to water-based whales with weak hind limbs and partial pelvises, and then eventually evolved to have "the bare remnants of a pelvis," only.
Hope this helps! Please let us know if you have any additional questions.
