Answer:
The correct answer is thymus gland.
Step-by-step explanation:
In the immune system, the thymus is considered as a primary lymphoid organ. Thymus is present behind the sternum, above the heart and between the two of our lungs. It is made up of two-lobed and is involved in releasing hormones and providing immunity.
Thymus is the primary site where T- cells become mature. T- cells are formed in bone marrow but reaches to thymus for maturation. These mature T- cells play a very important role in providing adaptive immunity against foreign molecules.
Thymus is larger till puberty and it slowly shrinks as the age increases. So the correct answer is thymus.