This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Anatomy
Most dangerous paicles causing pneumoconiosis are of size 
Select and explain. 
A. A. 1-5 micron, B. B. <1 micron, C. C. 5-15 micron, D. D. 10-20 micron
A: A. 1-5 micron
Answer: A: A. 1-5 micron 
Explanation: In pneumoconiosis, the most dangerous paicles range from 1-5 micron in diameter, because they may reach the terminal small airway and settle in there lining notes The solubility and cytotoxicity of paicles ,modify the nature of pulmonary response