This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
Phage typing is widely used for the intraspecies classification of one of the following bacteria: 
Select and explain. 
A. Staphylococci, B. E. coli, C. Kleb. Pneumoniae, D. Pseudomonas aeruginosa
A: Staphylococci
Answer: A: Staphylococci 
Explanation: Ans. is 'a' i.e., StaphylococciStaphylococcus strains are further differentiated into subspecies level on the basis of their bacteriophage susceptibility.