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.

  1. A. I and II only
  2. B. I and III only
  3. C. III only
  4. D. I, II and III

Correct Answer: B. I and III only

Explanation

The extremely thin epithelial lining and the rich network of blood capillaries directly facilitate the rapid diffusion of gases across the alveolar membrane.

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