Question

select the correct answer from each drop - down menu.
sharks, whales, and dolphins share similar features such as body shape and the position of fins. however, sharks have gills for breathing while whales and dolphins have lungs. these differences indicate that the organisms share a common ancestor for dropdown
whales also possess a vestigial pelvic bone. the presence of the pelvis bone may indicate that whales dropdown with options: have legs inside their bodies, evolved from organisms with legs, will have legs in the future
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Explanation:

1. For the first blank: Sharks (fish) and cetaceans (whales/dolphins, mammals) share similar body shapes due to convergent evolution (adapting to aquatic life), not a recent common ancestor. Their shared common ancestor was a very early, primitive organism before the split of fish and tetrapods, so the correct completion is traits evolved for aquatic life (implied by the context that the common ancestor is distant, with the similar features being independently evolved; the key is that the shared common ancestor is not the source of their aquatic traits, so the blank is best filled with the idea that the common ancestor was before their divergent respiratory adaptations, meaning the similar features are analogous, not homologous).
2. For the second drop-down: Vestigial structures are leftover traits from ancestral organisms that no longer serve their original function. A pelvic bone in whales is a vestige of ancestors that had legs, as whales evolved from land-dwelling mammals.

Answer:

1. (First blank completion) traits evolved independently for aquatic life (or more precisely, the common ancestor was a distant, non-aquatic organism, so the shared aquatic features are convergent; the most accurate fill-in is: their analogous aquatic body structures, not a recent ancestor (contextually, the phrase completes to: "These differences indicate that the organisms share a common ancestor for basic vertebrate traits, but their aquatic features evolved separately")
2. (Second drop-down selection) B. evolved from organisms with legs