Which of the following produces thymosin?

Thymosin is a hormone important for the development and differentiation of T-cells, which are crucial components of the immune system. The thymus gland, located in the upper chest behind the sternum, is specifically responsible for producing thymosin. This hormone plays a vital role in the maturation of T-cells from precursor cells that migrate from the bone marrow to the thymus. The other options, while related to immune functions—such as the spleen filtering blood and producing lymphocytes, and the tonsils acting as a first line of defense—do not have the same role in the production of thymosin. Thus, the thymus is the only gland in the body that synthesizes thymosin, making it the correct choice.