Which of the following nutrient is needed by our body for muscle-building?
(a) Carbohydrates
(b) Proteins
(c) Fats
(d) Dietary fibers

The correct option is (b):

Explanation of the correct option:

1. Proteins act as the building blocks of the body.
   
2. All the muscle filaments are made up of proteins and hence proteins act as the structure responsible for muscle building.
   
3. Therefore, intake of more protein in the diet helps with gaining muscles.
   

Explanation of the incorrect options:

Option (a):​

1. Carbohydrates act as the energy producing molecules of the body.
   
2. It is used for the production of energy during cellular respiration.
   

Option (c):

1. ​Fats are responsible for act as storage molecules for storage of energy in the adipocyte cells.
   
2. Fats are used when carbohydrate is depleted in the system.
   

Option (d):

1. Dietary fibres ​helps with proper digestion of nutrients.
   

Final Answer: Protein is needed by our body for muscle-building