The most highly concentrated source of energy in the body is a. proteins b. carbohydrates c. fats

The answer is B, carbohydrates. 

Carbohydrates are the first choice of the energy source of your body, they can be broken down into simple and soluble compounds such as glucose. These can be used by cells for respiration to generate energy for activities such as growth, movement, repair etc. Besides using for respiration, they are also capable of forming cell structures such as cellulose. 

That would be a working theory.