Concept:Proteins provide amino acids that the body uses for growth and tissue repair.
Explanation:During digestion, proteins are broken down into amino acids.
These amino acids are absorbed into the blood and carried to cells throughout the body.
The body uses them to build new cells and to repair damaged tissues.
This makes growth possible in young mammals and helps maintain healthy body parts in adults.
Although proteins can also form enzymes or hormones, the main dietary role described in the options is growth and cell repair.
Other options are incorrect because breaking down molecules is not the primary role of dietary proteins, and regulating chyme or serving as co-factors are not general dietary purposes.
Answer:A. promote growth and repair cells