Sleep is a difficult problem for dolphins because dolphins a. need more sleep than their predators b. must be awake and aware to breathe c. are unable to dream during sleep d. cannot swim while they are asleep

B. must be awake and aware to breathe

Explanation:

Sleep can be considered as unusual in dolphins. In dolphins during sleep only one hemisphere of the brain closes and the opposite side of the eye also get closed. The other eye remains open, and the other brain part remain functioning. This process facilitates in breathing during sleep as breathing and sleep cannot be simultaneous. Also the brain controls the response to the external stimuli during sleep.

2b2t

explanation:

2b2t

it doesn't. it was imagined up in the middle ages.