Final answer:
The thymus gland releases thymosin, which promotes the production of T cells in the immune system.
Step-by-step explanation:
The subject of this question is Biology since it pertains to the release of thymosin and the production of T cells in the immune system. Thymosins are hormones produced by the thymus gland, an organ involved in the immune system's development and differentiation of T cells. Thus, this question is related to the biological processes occurring in the body.