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
The preferred treatment option for primary syphilis is - 
Select and explain. 
A. Injection benzathine pencillin 2.4 million units IM single dose, B. Injection benzathine pencillin 2.4 million units IM once a week for 3 weeks, C. Cap. doxycycline 100 mg orally twice a day for 2 weeks, D. Tab. azithromycin 2 gm single dose
A: Injection benzathine pencillin 2.4 million units IM single dose
Answer: A: Injection benzathine pencillin 2.4 million units IM single dose 
Explanation: Ans. is 'a' i.e.,Injection benzathine pencillin 2.4 million units IM single dose