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
A patient develops an infection of methicillin-resistant Staphylococcus aureus. Which of the following drug cannot be used to treat the infection: 
Select and explain. 
A. Vancomycin., B. Cotrimoxazole., C. Cefaclor., D. Ciprofloxacin.
C: Cefaclor.
Answer: C: Cefaclor. 
Explanation: Cefaclor is a second generation cephalosporin and is not active against MRSA.