Answer:
Niacin (Ans. A)
Explanation:
Nicotinamide adenine dinucleotide (NAD) is known as important cofactor which help in carrying electrons from one reaction to another reaction in the cellular respiration process.
Cells are able to restore performed compounds which are containing a pyrimidine base precursor vitamin for the synthesis of NAD: nicotinamide, nicotinic acid, and nicotinamide riboside. 
These elements are taken up from the diet whos containing vitamin B3. Nicotinamide, and nicotinamide riboside both can be absorbed from the gut. Niacin or vitamin B3 also produced within cells with the help of cellular digestion of NAD+.
 
        
             
        
        
        
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This evidence suggest that all three living creatures that are mentioned have a common ancestor, even though they have been split into different types of groups of living organism millions of years ago. 
Science suggests that all of the living organisms on the planet have a common ancestor. Since we are talking about a common ancestor that lived few hundred million years ago, the living organisms split into different groups, and they do not resemble each other nowadays. The fruit fly is an insect, and the humans and mice are mammals, so they are into totally different groups, and it is easy to see by the genetic evidence that they are very distantly related, but the humans and mice are much more closely related because they belong to the same super family, and their connection is much more recent.
 
        
             
        
        
        
Answer:
It was discovered that the organisms in each of the five kingdoms have a different method of obtaining nutrients and are therefore fundamentally different.
Explanation:
New kingdoms were needed that reflected our growing knowledge of the differences between living organisms.