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
[{'content': 'All of the following are true regarding whooping cough except: \nSelect and explain. \nA. Spread by droplet infection, B. 90% of cases occur in children under 5 years of age, C. The whoop stage is more infectious than catarrhal stage, D. Blood count shows lymphocytosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans: cRef: Harrison, 16th ed, p. 875, 876', 'role': 'assistant'}]