Question

primary lymphoid organ; where t lymphocytes proliferate and mature... antigen lymphatic capillaries thymus

Explanation:

The thymus is a primary lymphoid organ where T - lymphocytes proliferate and mature. Antigens are substances that can trigger an immune response, and lymphatic capillaries are part of the lymphatic system for transporting lymph but are not the site of T - cell maturation.

Answer:

Thymus