which of the following statements is/ are correct regarding normal expiration?
(A) it is a passive process (B) it is an active process (C) The volume of thoracic cavity increases (D) The lower ends of the lungs are pulled downwards by the contraction of diaphragm
1) (A),(C) only
2) (A),(B) & (C) only
3) only (A)
4) (A),(C) & (D) only

Options

A. (A),(C) only
B. (A),(B) & (C) only
C. only (A)
D. (A),(C) & (D) only

Answer

To solve the question regarding normal expiration, we need to evaluate each statement provided:

1. **Statement (A): It is a passive process.**
- Normal expiration primarily occurs due to the relaxation of the diaphragm and elastic recoil of the lungs. This process does not require energy expenditure, making it a passive process.
- **Conclusion**: This statement is correct.

2. **Statement (B): It is an active process.**
- An active process would imply that energy is required for expiration. However, normal expiration is primarily a passive process as mentioned above.
- **Conclusion**: This statement is incorrect.

3. **Statement (C): The volume of thoracic cavity increases.**
- During normal expiration, the diaphragm relaxes and moves upwards, leading to a decrease in the volume of the thoracic cavity.
- **Conclusion**: This statement is incorrect.

4. **Statement (D): The lower ends of the lungs are pulled downwards by the contraction of the diaphragm.**
- This statement describes what happens during inspiration, not expiration. During expiration, the diaphragm relaxes and moves upwards, which compresses the lungs and pushes air out.
- **Conclusion**: This statement is incorrect.

Now, summarizing the evaluations:
- Only statement (A) is correct.
- Statements (B), (C), and (D) are incorrect.

**Final Answer: Option 3: only (A)**