An allergen is a(n)

A. Jaundice is caused by a buildup of bilirubin in the blood, typically due to liver or bile duct issues, not a blockage of lymph flow.
B. Edema occurs when there is an accumulation of fluid in tissues, which can result from a blockage in the lymphatic system (called lymphedema). This disrupts the normal drainage of lymph, causing swelling.
C. Varicose veins are swollen, twisted veins, typically caused by poor blood circulation, not lymphatic blockage.
D. Anemia is a condition where there is a deficiency of red blood cells or hemoglobin, and it is not related to a blockage of lymph flow.

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.