As we inhale air, oxygen enters the respiratory system and the circulatory system to transport it to the other parts of the body and to all cells. As the oxygen is already transported, the blood becomes deoxygenated and carries a CO2 which returns to the lungs and then we exhale the carbon dioxide.
        
             
        
        
        
The nucleotide variation is obtained by comparing nucleotide sequence between individuals between individuals of a particular population. If genetic variability is 0 % then the number of alleles would be 1. 
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What is genetic variability?</h3>
Genetic variability is the evolutionary process and development of new species. Genetic variability describes the dissimilarities such as brown eyes, blue eyes that happen naturally when DNA is altered.
Genetic variability varies in population. Genetic variability describes the tendency at which traits in a population may vary.
Gene variation refers to a differences in the genetic makeup of the individual. Genetic variation is a important process of natural selection and biological evolution.
Therefore, The nucleotide variation is obtained by comparing nucleotide sequence between individuals between individuals of a particular population. If genetic variability is 0 % then the number of alleles would be 1. 
To learn more about genetic variation, refer to the link :
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Answer: A
Evolution is the idea that species change over time, and natural selection is a mechanism by which evolution takes place.