13. What holds the two heavy chains of an immunoglobulin together?
A) Hydrophobic bonds
B) Salt linkages
C) Disulfide bonds
D) Hydrogen bonds

14. What is the term for the monovalent fragment with antigen-bindingactivity of an immunoglobulin?
A) H–L (heterodimer)
B) Fab (fragment antigen binding)
C) Heavy chain
D) Fc (fragment crystallizable)

15. What determines the class of an antibody?
A) The size of the antibody
B) The carbohydrate content
C) The heavy chains
D) The light chains

16. What are the two identical heavy and light chains of an  immunoglobulin linked together by?
A) Noncovalent interactions and disulfide bridges
B) Hydrogen bonds and disulfide bonds
C) Salt linkages and hydrophobic bonds
D) Salt linkages and hydrogen bonds