Final answer:
Air is warmed, humidified, and filtered in the nasal cavity to protect the delicate lung tissues from damage. Mucus and hairs trap particles in the air, preventing them from reaching the lungs.
Step-by-step explanation:
Air enters the respiratory system through the nasal cavity, where it is warmed, humidified, and filtered. The air is warmed to body temperature and humidified by moisture from mucous membranes, which helps reduce damage that cold, dry air can cause to delicate lung tissues. The air is also filtered as mucus and hairs in the nasal cavity trap particles in the air, preventing them from reaching the lungs.