Which one of the following statement is correct?

Options

A. Chest expands because air enters into the lungs
B. Air enters into the lungs because chest expands
C. The muscles of the diuphragm contracts because air enters into the lungs
D. All of the above statements are correct

Answer

To determine which statement is correct, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- The first statement claims, "The chest expands because air enters into it."
- This statement is incorrect. The chest expands due to the contraction of the diaphragm and intercostal muscles, which creates a negative pressure that allows air to enter the lungs.

2. **Evaluate the Second Statement:**
- The second statement states, "Air enters into the lungs because the chest expands."
- This statement is correct. When the diaphragm contracts and moves downward, the chest cavity expands, creating a lower pressure inside the lungs compared to the atmospheric pressure, allowing air to flow into the lungs.

3. **Evaluate the Third Statement:**
- The third statement says, "The muscle of the diaphragm contracts because air enters into the lungs."
- This statement is incorrect. The diaphragm contracts to create the space for air to enter the lungs, not the other way around.

4. **Evaluate the Fourth Statement:**
- The fourth statement claims, "All the above statements are correct."
- This statement is also incorrect since we have identified that the first, third, and fourth statements are wrong.

### Conclusion:
Based on the evaluation, the correct statement is the second one: "Air enters into the lungs because the chest expands."