The phagocyte termed dust cell is found in the:

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.

A. Naturally acquired active immunity occurs when the body is exposed to a pathogen, and the immune system produces its own antibodies in response. This type of immunity is not related to the transfer of antibodies from mother to fetus.
B. Artificially acquired active immunity involves vaccination, where the immune system is exposed to a weakened or inactivated pathogen to stimulate an immune response. This does not involve the transfer of antibodies from the mother.
C. Artificially acquired passive immunity involves the transfer of antibodies through medical interventions, such as antibody injections or serum treatments. While this involves passive immunity, it is not naturally occurring, nor is it related to placental transfer.
D. Naturally acquired passive immunity refers to the transfer of antibodies from mother to fetus through the placenta. These antibodies provide temporary protection to the newborn against infections, and this process is a natural example of passive immunity.