Answer:
A shark is not a mammal.
Step-by-step explanation:
Mammals are a classification of animals that are famously known for breathing oxygen/air, having fur/hair, mammary glands (which are responsible for the females' ability to produce milk for their young), and (usually) the live birth of their offspring.
Giraffes, dogs, and whales all have the qualities mentioned above. Sharks, however, do not.
Sharks are fish. Unlike the whale, which must go to the surface to breathe the necessary oxygen, sharks have gills. This possession of gills, and not lungs, allows them to breathe only underwater.
Since sharks can't breathe oxygen like mammals can, they are therefore not mammals.