Which of the following is a characteristic of simple proteins?

Simple proteins, also known as primitive or basic proteins, are composed solely of amino acid residues. This characteristic means that they do not contain any other non-protein components, which distinguishes them from conjugated proteins that include other molecules like carbohydrates or lipids.

When considering the options, it's important to note that simple proteins are fundamentally characterized by their composition of amino acids. Other options imply complexities or characteristics that are not true for simple proteins; for instance, stating that they contain multiple amino acids suggests a broader structure that fits within proteins in general, but does not define simple proteins. Similarly, saying they are synthesized in the body can apply to a variety of proteins, and asserting that they are always incomplete is not accurate, as some simple proteins can be complete, depending on the amino acids they contain.

Overall, recognizing that simple proteins consist exclusively of amino acids provides clarity on their classification and function.