Protein is used in repairing muscle, not only used in repairing muscle cells but also any kind of cells in our body.
Protein is used in producing hormones too. Some of hormones are made by lipid, but there are also hormones which are made by protein, called protein hormone.
Protein is used in making hemoglobin too. Hemoglobin consists of heme and globin. The globin part is made by a globular protein.
Protein isn't used in creating amino acids. It's the contrary, amino acids are used in creating protein.
So the answer is D
