Not completely sure, but maybe C.?
        
                    
             
        
        
        
Answer:
Nitrogen 
Explanation:
 
The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G), with hydrogen bonds to make double-stranded DNA.
 
        
             
        
        
        
Aquaporins would be expected to increase in numbers when there is an insufficient amount of water present in the blood.
Aquaporins are a type of proteins which are present in the integral membrane of the cells. They act as channels and help in the transport of water and small solutes across the membrane.
Whenever there is insufficient amount of water present in the blood, the antidiuretic hormone or the ADH responds. The aquaporins increase in number in the blood. They allow the transcellular reabsorption of water. Due to this fact, more water is able to escape from the collecting tubules and enter the blood. 
To learn more about aquaporins here
brainly.com/question/14570880
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The correct answer is A. Two populations of finches that cannot produce viable offspring 
Explanation:
Reproductive isolation is a biological and evolutionary phenomenon that prevents two species from successfully reproducing, this means they cannot produce offspring or the offspring is not fertile, even if these species had a common ancestor. Additionally, as a result of reproductive isolation, each species keeps its genes and features. This phenomenon is best exemplified in "Two populations of finches that cannot produce viable offspring " because this refer to the barriers for different species to reproduce or produce viable offspring, which is the focus of reproductive isolation.