Which nasal structure cleans and moistens the air entering the nasal cavity?

Correct option is A

Answer: (a) Conchae
Explanation:
The nasal conchae (turbinates) are bony structures inside the nasal cavity that play a crucial role in:
· Filtering dust and particles from inhaled air.
· Humidifying and warming the air before it reaches the lungs.
· Increasing airflow turbulence, which helps trap impurities in the mucus lining.
Other Options Explained:
· (b) Cilia:
· Tiny hair-like structures that move mucus and trapped particles out of the nasal cavity but do not directly humidify the air.
· (c) Sieve screen:
· This is not a recognized nasal structure related to air filtration.
· (d) Vertical septum:
· The nasal septum separates the nostrils but does not play a role in cleaning or humidifying air.
Conclusion:
Since conchae are responsible for cleaning, moistening, and warming incoming air, the correct answer is: (a) Conchae.