Sharks and dolphins look very similar. They have fins, mouths with teeth, and their skin feels the same. They both live in the ocean. They both also eat smaller fish. However, they are different in many, many ways. For instance, a dolphin is a mammal (like a human). It breathes air through its blowhole and can drown if it doesn't surface to breathe. A shark doesn't have to surface. It has gills that turn water into oxygen. Also, sharks are not mammals. They are fish. What other differences can you think of between sharks and dolphins?How does this author organize this passage?