This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
All of the following are categorized as secondary lymphoid organs except 
Select and explain. 
A. Lymph nodes, B. Spleen, C. Thymus, D. Subepithelial collec ons of lymphocytes
C: Thymus
Answer: C: Thymus 
Explanation: .