Which of the following is FALSE regarding aspects of the lymphatic system?
a. Primary lymphoid structures include red bone marrow and thymus, and they are places where lymphocytes are formed and mature.
b. The lymph nodes and tonsils are secondary lymphoid structures because they are places where lymphocytes initiate an immune response.
c. The spleen is a lymphoid structure that filters blood and is an organ where lymphocytes form and mature.
d. Lymph is produced when the interstitial fluid surrounding our cells is collected into lymphatic capillaries that merge into larger lymphatic vessels.