Assertion: Immune response of old persons become weak.
Reason: Thymus degenerates in old individuals.

Answer

A

Explanation

Thymus plays a major role in the development of the immune system. This gland secretes the peptide hormones called thymosins. Thymosins play a major role in the differentitation of T-lymphocytes, which provide cell-mediated immunity In addition, thymosins also promote production of antibodies to provide humoral immunity Thymus id degenerated in old individuals resulting in a decreased production of thymosins. As a result, the immune responses of old persons become weak.