…………acts as air conditions.

Explanation

**Step-by-Step Solution:**

1. **Identify the Structure:** The question asks about a structure that acts as an air conditioner in the respiratory system. The primary structure responsible for this function is the nasal cavity.

2. **Function of the Nasal Cavity:** The nasal cavity is lined with a mucous membrane. This membrane serves multiple purposes, including keeping the air we breathe moist. This moisture is essential for the respiratory system as it helps in the efficient exchange of gases.

3. **Filtration of Air:** The nasal cavity is equipped with tiny hairs, known as cilia. These hairs play a crucial role in filtering the air we inhale. They trap dust, dirt, and other particles, preventing them from reaching the lungs.

...