Explanation:
Explanation:

Inhalation (or inspiration) is the process of taking air into the lungs. During this process, the thoracic cavity expands to allow air to flow in. Here’s how it works:


What happens during inhalation in man:

1. Intercostal muscles contract
- This raises the ribs upward and outward.

2. Diaphragm contracts and flattens
- This increases the vertical dimension of the thoracic cavity.

3. Thoracic cavity volume increases
- As a result, the pressure inside the thoracic cavity decreases, creating a vacuum that draws air into the lungs.


Let's examine the options:

- A. The ribs are not raised – False
- The ribs are raised during inhalation to expand the chest.

- B. Diaphragm is raised – False
- The diaphragm is flattened (contracts) during inhalation.

- C. Intercostal muscles relax – False
- They contract to lift the ribcage.

- D. Pressure of the thoracic cavity increases – False
- The pressure actually decreases to allow air in.

- E. Size of thoracic cavity increases – True
- This is exactly what happens during inhalation.

Summary:
During inhalation, the size of the thoracic cavity increases due to the contraction of the diaphragm and intercostal muscles, allowing air to flow into the lungs.