Explanation:

- Collagen is a type of protein. It is abundant in the body and helps maintain the structure and strength of skin, bones, and connective tissues.

- Fats are essential nutrients, but they mainly serve as a source of energy and insulation for the body, not structure.

- Vitamins are organic compounds required in small amounts for various bodily functions and do not provide structural support.

- Carbohydrates are important for energy but do not contribute to the body's structural integrity like proteins do.

Your selection of option:3 - protein is indeed correct. .