In a research, it is proved that in old age one should take more quantity of proteins in diet than any other group of food. Which of the following justifies this?

• A.  Proteins help to repair and build muscles. In old age, muscle growth increases, hence protein intake should be more.
• B.      Proteins help to repair and build muscles. In old age, muscles become weak, hence protein intake should be more.
• C.      Proteins give energy to the body. In old age, the body needs more energy to work, hence protein intake should be more.
• D.      Proteins give energy to the body. In old age, the body uses stored fat hence, protein intake should be more.