With advancing age, the lymphatic system a. becomes less efficient at absorbing dietary lipids b. ceases to transport lymph c. produces an increasing number and variety of b-lymphocytes d. is less responsive to antigens

The right answer is D (less responsive to antigens)

It is proven that, after puberty, thymus activity (an organ that is included in the lymphatic system, producing T cells that pick up antigens) decreases and that in adult and aged people the thymus has no role. Work done in humans indicate that in fact the cellularity begins to decline from birth in favor of lymphocyte perivascular spaces and connective and adipose tissue, which leads to a decrease in the capture of antigens.

what subject is this

substitution is the answer in this case