1. The problem asks to classify pairs of structures as either homologous (HOMO) or analogous (ANA) and provide a one-sentence explanation. 2. Homologous structures are those that share a common ancestry and have similar bone structures but may have different functions. 3. Analogous structures have similar functions but evolved independently without a common ancestor, often due to convergent evolution. 4. For example, the human arm and dolphin's flipper are homologous because they share similar bone structures inherited from a common ancestor, despite different functions. 5. The human arm and bat's wing are also homologous for the same reason. 6. The horse's leg and human arm are homologous as they share a common skeletal framework. 7. Therefore, the classification for the pairs is HOMO with explanations based on shared ancestry and bone structure similarity. Final answer: - Human Arm and Dolphin's Flipper: HOMO (shared bone structure from common ancestor) - Human Arm and Horse's Leg: HOMO (common skeletal framework) - Human Arm and Bat's Wing: HOMO (similar bone structure despite different functions)