Question

lo 4.2. what is the respiratory membrane?
thick membrane that separates the air in the alveoli from the blood in the capillaries
the respiratory membrane refers to the lining of the trachea and bronchi.
the respiratory membrane is not involved in gas exchange.
thin membrane that separates the air in the alveoli from the blood in the capillaries.
thick membrane that separates the air in the alveoli from the blood in the capillaries.

Explanation:

The respiratory membrane is a thin membrane. Its main function is gas exchange. It separates the air in alveoli (tiny air - sacs in the lungs) from the blood in capillaries. The thinness of the membrane (composed of alveolar epithelium, capillary endothelium, and their fused basement membranes) allows for efficient diffusion of oxygen ($O_2$) into the blood and carbon dioxide ($CO_2$) out of the blood. The lining of the trachea and bronchi is ciliated epithelium for filtering and moving mucus, not the respiratory membrane. And the respiratory membrane is crucial for gas exchange, so options claiming it is thick or not involved in gas exchange are incorrect.

Answer:

Thin membrane that separates the air in the alveoli from the blood in the capillaries.