Final answer:
Connective tissue proteins like collagen are an example of a protein function, as they make up the tendons providing structural support.
Step-by-step explanation:
Proteins are essential macromolecules in living organisms and have a myriad of functions. They are polymers composed of amino acids linked by peptide bonds. The function of protein macromolecules can be structural, regulatory, contractile, or protective. Among the options provided, the one that represents a function of protein is D. Making up the connective tissue in tendons. Connective tissue proteins such as collagen provide strength and support to structures like tendons and ligaments. Other roles of proteins include enzymatic activity, transport, signaling, and being part of the immune response as antibodies.