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 diaphragm contracts because air enters into the lungs
D. All of the above statements are correct

Answer

To determine which statement is correct regarding the process of breathing, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Breathing Process**:
- Breathing involves the inhalation and exhalation of air. During inhalation, the diaphragm and intercostal muscles play a crucial role in expanding the chest cavity.

2. **Analyzing Each Statement**:
- **Statement 1**: "The chest expands because air enters into the lungs."
- This statement is misleading. The chest expands due to the contraction of the diaphragm and intercostal muscles, not because air is entering the lungs.

- **Statement 2**: "The air enters into the lungs because the chest expands."
- This statement is correct. When the chest cavity expands due to the contraction of the diaphragm and intercostal muscles, it creates a negative pressure that allows air to enter the lungs.

- **Statement 3**: "The muscle of the diaphragm contracts because air enters into the lungs."
- This statement is incorrect. The diaphragm contracts to create the space needed for air to enter the lungs, not because air is already present in the lungs.

- **Statement 4**: "All of the above statements are correct."
- Since Statements 1 and 3 are incorrect, this statement is also incorrect.

3. **Conclusion**:
- The only correct statement among the options provided is Statement 2: "The air enters into the lungs because the chest expands."

### Final Answer:
**The correct statement is: "The air enters into the lungs because the chest expands."**

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