(B) Thymus gland: enables immature lymphocytes to mature into T cells.
Explanation:
The thymus is an organ which is present between the lungs, behind the breastbone. It attains the status of an endocrine gland as it secretes a hormone thymosin. The thymus gland plays an important role in immunity. The immature lymphocyte formed in the bone marrow and moves to the thymus gland, where thymosin stimulates the maturation of lymphocytes or T cells.
