The correct answer is Option (1)- Thymus

The primary lymphoid organs are where lymphocytes (a type of white blood cell involved in the immune system) mature and develop. The primary lymphoid organs include the bone marrow and the thymus gland.

After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix. The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.