Alveoli is the part of the respiratory system which forms the site for an exchange of gases.
The exchange is essential to release out carbon dioxide and take in oxygen.
Alveoli being the site of gaseous exchange should have the essential features of a good respiratory surface which are -<em> thin, moist and enriched with blood vessels.</em>
Due to this, the alveoli are made up of a single layer of epithelial cell and has a network of capillaries surrounding it that carry blood to facilitate the exchange the gases.
I think the correct answer from the choices listed above is option A. It is the alveoli that is composed of single layer <span>surrounded by a network of capillaries. These are used to allow oxygen and carbon dioxide to move from the lungs to the bloodstream.</span>
The selenium particles when coated on paper towels were extremely effective and continuously inhibited (about a 90% reduction) the growth of gram-positive bacteria including S. aureus and S. epidermidis after 24, 48, or 72 hours.
