<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:An investigator is studying the clearance of respiratory particles in healthy non-smokers. An aerosol containing radio-labeled particles that are small enough to reach the alveoli is administered to the subjects via a non-rebreather mask. A gamma scanner is then used to evaluate the rate of particle clearance from the lungs. The primary mechanism of particle clearance most likely involves which of the following cell types?? A: Goblet cells, B: Club cells, C: Type I pneumocytes, D: Macrophages, E: Neutrophils,  <response>: This question is asking about the primary mechanism of particle clearance from the lungs. The particles described are small enough to reach the alveoli. The main cell types in the alveoli are type I and type II pneumocytes and alveolar macrophages. Of these, alveolar macrophages play the biggest role in clearing particles and pathogens from the alveolar space. Type I pneumocytes are very thin epithelial cells that facilitate gas exchange. Type II pneumocytes secrete surfactant. Goblet cells and club cells are found in the conducting airways, not the alveoli. Neutrophils can be recruited to the alveoli during inflammation but are not the primary clearance cell. Therefore, the primary clearance mechanism most likely involves alveolar macrophages.D: Macrophages 