This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Russell's bodies are found in: 
Select and explain. 
A. Activated macrophages, B. Histiocytes, C. Plasma cells, D. Erythrocytes
C: Plasma cells
Answer: C: Plasma cells 
Explanation: None