21. Which of the following statements regarding immunoglobulin light chains is correct? (A) k (kappa) associates with only particular heavy-chain isotypes (B) Agiven antibody may contain just k (kappa), or justλ (lambda), or both (C) Most antibodies in humans contain 2. (lambda) light chains (D) There is no functional difference between x (kappa) andλ (lambda) (E) Light chains possess only framew work regions, not hypervariable regions