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: Medicine
[{'content': 'A drug is to be delivered by a nebuliser. The size of a droplet for its humidification is : \nSelect and explain. \nA. < 5m, B. 10-May, C. 15-Oct, D. 15-20', 'role': 'user'}, {'content': "Answer: A \nExplanation: Answer is A (< 5 m): 'Paicles of size < 2.5 mm can he carried to the lower airways. 'Paicles with size above 10-15 mm in diameter, because of their settling velocities in air, do not penetrate beyond the upper airways' 'Paicle of size 2.5-10 mm deposit relatively high in the tracheobronchial tree.' 'Paicles of size < 2.5 mm can be carried to the lower airways.'", 'role': 'assistant'}]