This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunomodulator, Subject name: Pharmacology
Which is an immuno stimulant: 
Select and explain. 
A. Methimazole, B. Levamizole, C. Ketoconazole, D. Zidovudine
B: Levamizole
Answer: B: Levamizole 
Explanation: bRef: KDT, 5th ed, p. 763 & 4th ed, p. 821