The human lymphatic or lymphoid system is part of the immune system. A network of lymphatic vessels throughout the body brings clear lymph fluid from the tissues one way back to the heart. Along the way the lymphatics pass through lymphoid tissue that is present in lymph nodes as well as lymphoid tissue present in several areas throughout the body. For example, lymphoid tissue is present along the digestive system. Accessory organs such as the tonsils contain lymphoid follicles.
Another part of the lymphoid system is that concerned with the production and circulation of lymphocytes, the cells that are responsible for immune functions. These organs include the spleen, thymus and bone marrow.
Thus, the answer to your question is “D. Thyroid”. The others are part of the lymphoid system.