How does the fossil record of whales illustrate the transition from terrestrial to aquatic life?

• A. Fossils indicate whales have always been aquatic without any terrestrial ancestors.
• B. Whales' fossil record shows a sudden change from land to water with no intermediate forms.
• C. Fossils show gradual adaptations such as limb modifications and changes in spine structure.
• D. The fossil record lacks any evidence linking whales to terrestrial life.

Answer: (C)