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: Pharmacology
Drug of choice for primary syphilis is : 
Select and explain. 
A. Ampicillin, B. Benzathine penicillin, C. Erythromycin, D. Tetracycline
B: Benzathine penicillin
Answer: B: Benzathine penicillin 
Explanation: None