Assertion :- Air sacs in Aves are connected to lungs and supplement in respiration.
Reason :- It increases the area of gaseous exchange.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

To solve the question regarding the assertion and reason related to air sacs in Aves (birds), we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Air sacs in Aves are connected to lungs and supplement in respiration."
- This statement is true. Air sacs are indeed a part of the respiratory system in birds and play a crucial role in respiration by facilitating a continuous flow of air through the lungs.

2. **Understanding the Reason**:
- The reason provided is that "It increases the area of gaseous exchange."
- This statement is also true. The presence of air sacs allows for a larger surface area for gas exchange, which enhances the efficiency of respiration in birds.

3. **Connecting Assertion and Reason**:
- Both the assertion and the reason are correct.
- The reason explains why the assertion is true: the air sacs increase the surface area available for gas exchange, which is essential for the high metabolic demands of birds.

4. **Evaluating the Options**:
- We need to determine which option correctly describes the relationship between the assertion and reason.
- The first option states that both the assertion and reason are true, and the reason is the correct explanation of the assertion. This aligns with our analysis.

5. **Conclusion**:
- Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
- The correct option is: **Both assertion and reason are true, and reason is the correct explanation of assertion.**

---