Mark the correct pair of muscles involved in the normal breathing in humans.

Options

A. Extemal and internal intercostal muscies
B. Diaphragm and abdominal muscles
C. Diaphragm and external intercostal muscles
D. Diaphragm and intercostal muscles

Explanation

To solve the question about the correct pair of muscles involved in normal breathing in humans, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Normal Breathing**: Normal breathing consists of two main processes:
- **Inspiration** (breathing in) where oxygen is taken into the lungs.
- **Expiration** (breathing out) where carbon dioxide is expelled from the lungs.

2. **Identify the Main Muscles Involved**:
- The **Diaphragm**: This is a dome-shaped muscle located at the base of the thoracic cavity. It plays a crucial role in the process of inspiration by contracting and flattening, which increases the volume of the thoracic cavity and reduces pressure, allowing air to flow into the lungs.
- **Intercostal Muscles**: These are the muscles located between the ribs. They assist in the breathing process by expanding and contracting the rib cage during inhalation and exhalation. There are two types:
- **External Intercostal Muscles**: These help in elevating the ribs during inhalation.
- **Internal Intercostal Muscles**: These are primarily involved in forced expiration.

3. **Evaluate the Options Provided**: The options given are:
- A) External and Internal Intercostal Muscles
- B) Diaphragm and Abdominal Muscles
- C) Diaphragm and External Intercostal Muscles
- D) Diaphragm and Intercostal Muscles

4. **Select the Correct Pair**:
- The most accurate answer is **D) Diaphragm and Intercostal Muscles**. This is because the diaphragm is essential for inspiration, and the intercostal muscles (both external and internal) assist in the overall breathing process.

### Final Answer:
The correct pair of muscles involved in normal breathing in humans is **Diaphragm and Intercostal Muscles (Option D)**.

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