Final answer:
The correct traits a land mammal might evolve to live in the ocean are fins for swimming, a blowhole for breathing, and the ability to hold breath for extended periods, as exemplified by whales and dolphins.
Step-by-step explanation:
When considering a land mammal evolving over time to live in the ocean, it is important to consider the traits that would be beneficial for aquatic life. The traits that such a mammal might evolve would be those that aid in swimming, diving, and managing the aquatic environment. Specifically, a mammal might evolve characteristics such as fins for propulsion, a blowhole for breathing at the surface without having to fully emerge, and the ability to hold its breath for extended periods to allow for deep or prolonged dives. These traits are observable in modern marine mammals like whales and dolphins, which evolved from land-dwelling ancestors but have adapted to the oceanic environment. Other adaptations can include a streamlined body to reduce drag in the water, layer of blubber for insulation, and changes in locomotion to suit water rather than land. Therefore, the correct answer is C) Fins, a blowhole, and the ability to hold breath for long periods of time. This is because these traits are aligned with the demands of an aquatic lifestyle and are traits actually found in aquatic mammals that evolved from land-dwelling ancestors.