Select the correct statement .

Options

A. The contraction of internal intercostal muscles lifts up the ribs
B. The RBCs transport oxygen only
C. The thoracic cavity is anatomically an air tight chamber
D. Healthy man can inspire approximately 5000 mL of air per minute

Answer

To solve the question "Select the correct statement," we will analyze each option provided and determine which one is accurate.

### Step-by-Step Solution:

1. **Analyze the first statement**:
- The statement claims that the contraction of the internal intercostal muscles lifts up the ribs.
- This is incorrect because the internal intercostal muscles are primarily involved in forced expiration, which decreases the thoracic cavity's volume by pulling the ribs downward and inward.

**Hint**: Remember that the internal intercostal muscles assist in expiration, not inspiration.

2. **Analyze the second statement**:
- The statement suggests that red blood cells (RBCs) transport only oxygen.
- This is also incorrect. RBCs transport oxygen from the lungs to the tissues and carry carbon dioxide from the tissues back to the lungs for exhalation.

**Hint**: Consider the dual role of red blood cells in gas exchange.

3. **Analyze the third statement**:
- The statement claims that the thoracic cavity is anatomically an airtight chamber.
- This statement is misleading. While the thoracic cavity is relatively sealed, it is not completely airtight due to the presence of structures such as the trachea and esophagus, which allow for airflow and other functions.

**Hint**: Think about the structures that pass through the thoracic cavity and their implications for airtightness.

4. **Analyze the fourth statement**:
- The statement states that a healthy man can inspire approximately 5000 ml of air per minute.
- This is incorrect. A healthy adult typically has a tidal volume of about 500 ml per breath, and the total volume of air inspired in a minute (minute ventilation) would depend on the respiratory rate. However, the figure of 5000 ml is not accurate for a single breath.

**Hint**: Recall the average tidal volume and how it relates to breathing rate.

### Conclusion:
After analyzing all the statements, none of the options provided are correct. However, if we were to select the least incorrect statement, it would be the one regarding the thoracic cavity, but it still has inaccuracies. Therefore, based on the analysis, it appears that all options are flawed.

**Final Answer**: None of the statements are correct.