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: Social & Preventive Medicine
Prophylaxis for health personnel working in a plague ward is -a) Vaccineb) Tetracycline throughout the dutyc) A cource of tetracyclined) Vaccine and Erythromycine) Observation 
Select and explain. 
A. ac, B. a, C. ab, D. bc
C: ab
Answer: C: ab 
Explanation: None