Which among the following statement is correct ?

The primary lymphoid organs are bone marrow and thymus . Malignant tumors normally remain confined to their original location . A widely used diagnostic test for AIDS is widal test. Heroin is obtained by methylation of morphine .

The primary lymphoid organs are bone marrow and thymus .

The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes. After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix .