Answer:
The fossil record contains many intermediate stages between their early, land dwelling common ancestor and modern whales and hippos.
Step-by-step explanation:
I would say this one makes the most sense.
B) Hippos are land-dwelling mammals that spend much of the day walking on the bottom of bodies of water.
This one doesn't explain how the are related so we can cross this out.
C) Whales are classified as mammals even though they have a very sparse amount of hair on their skin.
Although this is true, it really doesn't prove how they are related to Hippos.
D) Whales and other marine mammals are the only groups of mammals to have limbs that are modified as flippers as well as a streamlined body shape.
This statement is also true but does not explain how hippos and whales are related in anyway.
This leaves us with A.