The Great Barrier Reef is amazing but we must always remember that we are in another world when we are underwater on SCUBA. We need to breathe air. Unlike the fish and corals, we carry our air with us in a tank on our back. "What's happening with my air," said Dan the Diver. "There are bubbles everywhere. I need to surface but not in a hurry." Dan knew that air expands as it rises in the water and his lungs would do the same. He should be...