Final answer:
The claim that mature T cells only circulate for 3-4 days in the absence of their specific antigen is false; T cells and B cells can survive much longer, potentially for years, as naïve or memory cells. The correct option is b.
Step-by-step explanation:
The statement that mature T cells only continue their circulation for 3-4 days in the absence of their specific antigen is false. Once they have matured, both T cells and B cells patrol the body for much longer periods of time in search of their specific antigen. When the antigen is not encountered, these naïve B and T cells can survive in the body for years, despite not being activated.
Upon activation, most T cells and B cells do die once the pathogen has been cleared. Nonetheless, memory T cells and memory B cells remain and can last for years, ready to mount a quick response should the same antigen be encountered again. This long-term survival contributes to the body's acquired immunity.
Hence, Option b is correct.