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.
Hydrogen bonds connecting base pairs must be broken.
All you need is to locate an artery. theres one by your neck, on the the far sides of your wrists, between your thighs, or you could just feel your own heart.
