Final answer:
Dinosaurs, despite their bird-like features and being ancestors to birds, are classified with reptiles, within the broad group of diapsids known as archosaurs. Birds evolved specifically from theropod dinosaurs within the Saurischia, not from the Ornithischia which have "bird-hipped" structures. The modern classification reflects evolutionary history, with birds being a specialized subgroup of reptiles,the correct option is B).
Step-by-step explanation:
Dinosaurs were very bird-like, but we continue to classify them with reptiles. This classification places them in a broader group of diapsids known as archosaurs, a category that also includes modern birds as well as extinct groups like pterosaurs. Despite being bird-like in many aspects, and being the direct ancestors of birds, dinosaurs are still categorized within the reptile domain primarily due to historical and anatomical reasons.
It's important to note that birds evolved from a specific group of theropod dinosaurs within the clade Dinosauria, which is subdivided into Saurischia ("lizard hips") and Ornithischia ("bird hips"). Contrary to what their names might suggest, birds did not evolve from the "bird-hipped" ornithischians but rather from the "lizard-hipped" saurischian lineage. Within the Saurischia, the bipedal predators called theropods are the group that eventually gave rise to birds. This lineage shows numerous similarities with birds, like in the structure of the hip and wrist bones, and the presence of the wishbone formed by the fusion of clavicles.
In the traditional division of amniotes, the classes were Mammalia, Reptilia, and Aves. However, this scheme has been updated with our current understanding that birds are a specialized subgroup of the reptiles, descending from the theropod dinosaurs. Therefore, while birds are considered separately for convenience and due to some distinctive features, scientifically they are still a part of the overarching reptilian clade.