Which of the following is a function of protein?

Proteins play a crucial role in various bodily functions, making option "all of the above" the correct answer. Muscle repair is a vital function of proteins; they are essential for the repair and growth of muscle tissue after exercise or injury.

Proteins also function as enzymes, which are crucial for catalyzing biochemical reactions in the body. These enzymes speed up reactions that are necessary for digestion, metabolism, and other processes.

Additionally, proteins are involved in hormone production. Many hormones are proteins or peptides that regulate different physiological functions, including growth, metabolism, and mood.

Thus, the functions of protein encompass muscle repair, enzyme function, and hormone production, confirming that the correct answer encompasses all these critical roles.