Which of the following is most related to the placental transfer of antibodies from the mother to the fetus?

A. The spleen does not shrink after puberty. It remains an active part of the immune and blood filtration systems throughout life.
B. The thymus (note: it appears misspelled as "Thygus" in the question) is the correct answer. It plays a crucial role in the development of T lymphocytes (T cells) during childhood but begins to shrink and become replaced by fatty tissue after puberty—a process known as involution.
C. The liver does not shrink after puberty. In fact, it continues to grow and function in metabolism, detoxification, and digestion throughout a person’s life.
D. The cisterna chyli is a dilated sac at the lower end of the thoracic duct involved in lymphatic drainage. It does not shrink after puberty and remains functional throughout life.

A. Autoimmunity is a malfunction of the immune system where the body attacks its own tissues — it is not a type of protective immunity acquired through infection or exposure.
B. Species immunity refers to natural resistance to certain diseases that affect other species (e.g., humans not being susceptible to some animal viruses), not immunity acquired through infection.
C. Passive immunity involves receiving antibodies from another source (like from mother to baby or via antibody-containing injections) and does not require the immune system to produce its own response.
D. Active immunity is the correct answer. It develops when the body is exposed to a pathogen or its toxins and responds by producing its own antibodies and memory cells, providing long-term protection.