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
In a patient of orbital cellulitis, micro organism on culture show greenish colonies and optochin sensitivity. The most likely organism is : 
Select and explain. 
A. Strep. viridans, B. Staphylococcus, C. Pseudomonas, D. Pneumococcus
D: Pneumococcus
Answer: D: Pneumococcus 
Explanation: “Pneumococci is optochin sensitive and forms green colonies on blood agar due to Α hemolysis.”
Characteristic features of Pneumococci :

Bile soluble, optochin sensitive
Inulin fermenter
Capsulated, shows quellung reaction
Colonies show central umbonation, appear as draughtsmann or carrom coin
MC causative agent of lobar Pneumonia, Adult meningitis, otitis media, sinusitis (orbital cellulitis is complication of sinusitis).