Answer:
The correct option is <u><em>A. they evolved from land mammals.</em></u>
Explanation:
The process of evolution explains how closely one organism is to another based on their common ancestors. Scientists believe that those organisms which show many similarities in their structures or functions might have evolved from a common ancestor in the past.
As in the above-mentioned question, scientists have observed that cetaceans lack gills and breath air, this is a property of land mammals. The cetaceans have fin bones which are similar to the limb bones. As limb bones are present in land mammals, hence they cetaceans and land mammals might have common ancestors in the past.
The earth's inner core is the innermost layer of the earth. Primarily, it is a solid ball composed of an iron-nickel allow and some other elements, which holds a radius of about 1,220 kilometers.
Answer: Base pairs occur when nitrogenous bases make hydrogen bonds with each other.
Explanation: Each base has a specific partner: guanine with cytosine, adenine with thymine (in DNA), The hydrogen bonds are weak allowing it to "unzip"
