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
[{'content': 'Paul Bunnell antibodies are reactive in all except- \nSelect and explain. \nA. OX, B. Sheep, C. Dog, D. Horse', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]