Which of the following best describes what alveoli are? a. they are the smallest tubes in the respiratory system. b. they have a small amount of surface area. c. they are found on the end of bronchioles. d. they are comprised of millions of cells. select the best answer from the choices provided.

The correct answer is C. They are found on the end of bronchioles.

Explanation:

Alveoli are the sac-like structures that are formed by the terminal bronchioles so alveoli are the terminal structures through which many air sacs are raised called alveoli which helps in the transport and exchange of CO₂ and O₂ between lungs and blood.

Blood capillaries surround each alveolus and carbon dioxide moves from blood present in these capillaries to alveoli because the partial pressure of carbon dioxide is higher in blood capillaries than in alveoli and oxygen moves from alveoli to blood because the partial pressure of oxygen is higher in alveoli than blood.

Therefore the correct answer is C. They are found on the end of bronchioles.