Determine the correctness or otherwise of the following Assertion (a) and the Reason (r): Assertion: IgM is found in serum as a pentameric protein consisting of five IgM monomers. Reason: The pentameric form of IgM is due to cross-linking of IgM monomers via peptide bond. Options: (A) both (a) and (r) are true and (r) is the correct reason for (a) (B) both (a) and (r) are true but (r) is not the correct reason for (a) (C) (a) is true but (r) is false (D) (a) is false but (r) is true