As air passes through the nasal cavity, it is

Options

A. Filtered in the nostrils
B. Moistened by mucus
C. Warmed to the body temperature
D. All of these

Explanation

### Step-by-Step Solution:

1. **Understanding the Path of Air**:
- Air enters the respiratory system through the nostrils.
- It then travels through the nasal cavity and into the nasopharynx before moving further into the respiratory tract.

2. **Functions of the Nasal Cavity**:
- The nasal cavity serves as a conducting zone for air.
- Its primary functions include filtering, moistening, and warming the air before it reaches the lungs.

3. **Filtering the Air**:
- The hair present in the nostrils acts as a filter, trapping dust particles and germs.
- This prevents harmful substances from entering the respiratory system.

4. **Moistening the Air**:
- The mucous membranes in the nasal cavity secrete mucus, which moistens the incoming air.
- This is important because dry air can irritate the respiratory tract.

5. **Warming the Air**:
- The blood vessels in the nasal cavity help to warm the air to body temperature.
- This ensures that the air is at an appropriate temperature for the lungs to handle.

6. **Conclusion**:
- As air passes through the nasal cavity, it is filtered, moistened, and warmed.
- Therefore, the correct answer to the question is: **All of these (option D)**.