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
[{'content': 'A 36 years old woman recently treated for leukemia is admitted to the hospital with malaise, chills and high fever. Gram stain of blood reveals the presence of gram-negative bacilli. The initial diagnosis is bacteremia and parenteral antibiotics are indicated. The record of the patient reveals that she had a severe urticarial rash, hypotension and respiratory difficulty after oral penicillin V about 6 months ago. The most appropriate drug should be : \nSelect and explain. \nA. Ampicillin plus Sulbactam, B. Aztreonam, C. Cefazolin, D. Imipenem plus cilastatin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]