The correct answer is B. Sensitive period
Explanation:
In development, the sensitive period refers to a lapse of time in which organisms are more susceptible or receptive to stimuli and therefore during this time there can be great advances in development. Additionally, different from critical periods sensitive periods do not imply irreversible consequence if the stimuli are not presented. For example, in human beings from birth to the age of 6 years, children are more receptive to learn and acquire certain skills such as learning a new language if exposed to it and therefore this can be considered as a sensitive period. Considering this, it can be concluded the definition presented refers to the Sensitive period.
 
        
             
        
        
        
A monomer made up of a nitrogenous base, a five-carbon sugar, and a phosphate group bonded together.
        
                    
             
        
        
        
I believe the answer is c)
        
                    
             
        
        
        
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+.