Why Do Adults Become More Susceptible to Disease as They

Why do adults become more susceptible to disease as they age?

A) Fewer antibodies are produced and T cells become less efficient.
B) More B cells and T cells are produced than can be absorbed by the bone marrow and the thymus gland.
C) The thymus gland and the bone marrow produce antibodies that attack normal body cells.
D) The thymus gland becomes excessively large and interferes with the production of B cells.