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: Microbiology
A infant had high grade fever and respiratory distress at the time of presentation to the emergency room. The sample collected for blood culture was subsequently positive showing growth of a haemolytic colonies. On Gram staining these were gram positive cocci. In the screening test for identification, the suspected pathogen is likely to be susceptible to the following agent - 
Select and explain. 
A. Bacitracin, B. Novobiocin, C. Optochin, D. Oxacillin
C: Optochin
Answer: C: Optochin 
Explanation: None