This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Medicine
What is the diagnosis in this patient who appeared sick, had a bull neck, and was tachycardic? 
Select and explain. 
A. Diphtheria, B. Epiglottitis, C. Infectious mononucleosis, D. Rheumatic fever
A: Diphtheria
Answer: A: Diphtheria 
Explanation: Answer A. DiphtheriaThe patient's features are typical of diphtheria. Her throat culture was positive for Corynebacterium diphtheriae. The patient recovered after the initiation of treatment with penicillin.