This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic histology, Subject name: Anatomy
In which of the following sites do lymphocytes become immunocompetent? 
Select and explain. 
A. Germinal center of secondary lymphoid nodules, B. White pulp of the spleen, C. Thymic coex, D. Red pulp of the spleen
C: Thymic coex
Answer: C: Thymic coex 
Explanation: T lymphocytes mature and become immunocompetent in the coex of the thymus, B lymphocytes mature and become immunocompetent in the bone marrow. After an antigenic challenge, lymphocytes proliferate and differentiate in various lymphoid tissues