The order Cetacea includes modern-day whales, dolphins, and porpoises. These marine mammals share common characteristics that have led scientists to make a conclusion about their evolutionary history. Cetaceans:

lack gills and must breathe air

give birth to live young rather than lay eggs

have fin bones that are similarly shaped to limb bones

have spines that flex up and down rather than side to side

The characteristics of cetaceans provide evidence that

A. they evolved from land mammals.

B. the theory of evolution is incorrect.

C. they evolved from air-breathing fish.

D. the bodies of their ancestors never changed.

The correct option is A. they evolved from land mammals.

Explanation:

Evolution can be described as a process through which organisms in a species change over a period of time due to the natural selection of the environment. Those organisms that have many similarities in their functions or structures are considered closer to one another and have the same common ancestors.

The properties mentioned in the question about cetaceans resembles the properties of land mammals. For example, cetaceans lack gills and breathe air. Land mammals also do not have gills and need to respire for living. The cetaceans have fin bones which are similar to the limb bones in the land mammals. Hence, these observations show that cetaceas have evolved from land mammals.