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.
<span>Fossils, or the fossilized remains of an animal, tend to be bones which are made of much denser materials than flesh. Since a jellyfish has no bones, a bony fish is more likely to leave a fossil.</span>
