Which of the following properties of alveoli is/are helpful in gaseous exchange during respiration in human beings?

I. The epithelial lining of alveoli is very thin.

II. Elastic fibres are present in alveolar wall.

III. Wall of alveoli is surrounded by many blood capillaries.

Select the correct answer using the code given below.

All three properties are essential adaptations for efficient gas exchange in the lungs:

• Thin Epithelial Lining: The alveolar walls are composed of a single layer of squamous epithelial cells. This extremely thin barrier minimizes the diffusion distance for O2 and CO2.
• Elastic Fibres: These fibres allow the alveoli to stretch during inhalation, which increases the surface area for exchange, and recoil during exhalation to help expel air. This flexibility is vital for maintaining the structural integrity and ventilation required for exchange.
• Blood Capillaries: The alveoli are enveloped by a dense network of capillaries. This ensures that deoxygenated blood is constantly brought to the lungs and oxygenated blood is carried away, maintaining the steep concentration gradient necessary for passive diffusion.