How Do Dolphins Sleep If They Must Regularly Come to the Water's

Multiple Choice

How do dolphins sleep if they must regularly come to the water's surface to breathe?

A) Only one brain hemisphere sleeps at a time.
B) Both hemispheres sleep at the same time but the sleep is light.
C) They retain air in their lungs and stay at the surface to breath while sleeping.
D) They do not come to the surface while sleeping, but instead obtain oxygen through their skin.