Lung capillaries are so narrow that RBCs must pass through them in single file. This feature aids respiration by:A.increasing the production of CO2 in the RBCs.B.allowing RBCs to have direct contact with alveoli.C.giving maximum exposure of each RBC to diffusing gases.D.making Hb available for CO2 but not O2 to bind.

The correct answer is C. giving maximum exposure of each RBC to diffusing gases.

Here's the step-by-step explanation:

1. The lung capillaries are extremely narrow, which forces red blood cells (RBCs) to pass through them in a single file.

2. This arrangement ensures that each RBC is exposed to the wall of the capillary, which is where gas exchange occurs.

3. The gases (oxygen and carbon dioxide) diffuse across the capillary wall and the cell membrane of the RBCs. This process is called respiration.

4. By passing through in single file, each RBC has maximum exposure to the diffusing gases. This allows for efficient oxygen uptake and carbon dioxide removal.

5. Therefore, the narrowness of lung capillaries aids respiration by giving maximum exposure of each RBC to diffusing gases.