Answer:
A dolphin breathes through a single blowhole on the top surface of its head. The blowhole is covered by a muscular flap, which provides a watertight seal.
A dolphin holds its breath while below water.
The dolphin opens its blowhole and begins to exhale just before reaching the surface of the water. To open the blowhole, the dolphin contracts the muscular flap.
Step-by-step explanation: