Many people think that dolphins are fish, but this is not ___. Dolphin are different from fish in many important ways. They are mammals. They are __- blooded, and they cannot stay underwater all the time like __. They breathe air. They have to come to the ___ of the water and take in air every few minutes. Dolphins are very friendly to people, and they are helpful too. A few dolphins have already been ___ to do useful things. They ___ messages quickly between ships, they find lost objects in the ocean, and they carry equipment underwater to collect information for ___. In the future dolphins could become the most ____ animals in the world.