An organ that shrinks after puberty is the:

A. Neutrophils are a type of white blood cell that primarily responds to bacterial infections and perform phagocytosis, not specifically attacking tumor or virus-infected cells.
B. Regulatory T cells help regulate the immune response and prevent excessive immune activity, but they do not directly attack tumor or virus-infected cells.
C. Natural killer (NK) cells are a type of lymphocyte that plays a key role in the body's defense against tumor cells and virus-infected cells by directly attacking and destroying them.
D. Memory T cells are responsible for "remembering" a previous pathogen, enabling a quicker response upon future exposure, but they do not directly attack tumor or virus-infected cells.

A. They have thin walls – Lymphatic vessels have thin walls, similar to veins, which allow for the passage of lymph.
B. They can contract to propel lymph – Lymphatic vessels do have the ability to contract, aided by smooth muscle and valves, which helps propel lymph in the right direction.
C. They transport lymph to the tissues – This statement is incorrect. Lymphatic vessels carry lymph away from the tissues (not to the tissues) and toward lymph nodes and eventually to the bloodstream.
D. They are blind-ended – Lymphatic capillaries are indeed blind-ended, meaning they begin as closed-ended tubes that absorb interstitial fluid from tissues.