Which of the following statements best characterizes an antibody?

• A. An antibody contains high molecular weight RNA as its basic structure
• B. An antibody is composed of protein and cannot be distinguished from the albumin fraction of the serum proteins.
• C. An antibody is composed of four identical protein subunits which may be caused to dissociate by treatment with urea.
• D. An antibody contains protein as its major chemical component and its synthesis may be elicited by the administration of a foreign protein or polysaccharide.