Final answer:
The majority of cells in the alveoli are squamous epithelial cells (D). Type I alveolar cells are responsible for gas exchange.
Step-by-step explanation:
The majority of cells in the alveoli are squamous epithelial cells (D).
Type I alveolar cells are the major cell type in the alveolar wall, constituting up to 97 percent of the alveolar surface area. These cells are highly permeable to gases and are responsible for gas exchange.
The alveoli also contain type II alveolar cells that secrete pulmonary surfactant to reduce surface tension, and alveolar macrophages that remove debris and pathogens.
The majority of cells in the alveoli are squamous epithelial cells, also known as type I alveolar cells. These cells are essential for gas exchange due to their thinness and large surface area, covering up to 97% of the alveolar surface. They are designed to be highly permeable to gases, allowing for efficient transfer of oxygen into the blood and carbon dioxide out of the blood.