Which structure of the lymphatic system maintains its importance throughout life? bone marrow tonsils thymus adenoids

I think the answer is bone marrow. 
The bone marrow is the source of all lymphocytes also known as a lymphoid organ. It produces stem cells that would become type T and B lymphocytes when they mature. These lymphocytes strengthen the body's immune system. 
The type B cells that would develop, remains in the bone marrow while the type T will go to the thymus.