Final answer:
Dolphins and whales are mammals, so they have lungs and breathe air. They come to the surface of the water to take a breath through their blowholes.
Step-by-step explanation:
Dolphins and whales are mammals, which means they have lungs and breathe air, just like humans. They do not have gills like fish. When dolphins and whales come to the surface of the water, it is because they need to take a breath. They have a blowhole on top of their heads which they use to inhale air.