Which of the following sequences correctly represents the layers of the alimentary canal from the most visceral (deep) to the most superficial (surface)?

A. Type I pneumocytes: The respiratory membrane is formed by alveolar Type I (squamous) pneumocytes, their basement membrane fused with the capillary basement membrane, and capillary endothelial cells -allowing efficient gas diffusion.
B. Respiratory bronchioles: Respiratory bronchioles are airway structures leading to alveoli but are not the cellular layer that composes the thin respiratory membrane.
C. Segmental (tertiary) bronchi: These are larger conducting airways far upstream from the alveolar gas-exchange surface.
D. Type II pneumocytes: Type II cells produce surfactant and are present in alveoli, but the thin gas-exchange surface is primarily Type I pneumocytes (Type II are cuboidal and thicker).

A. Tubular secretion involves the reabsorption of substances from the renal tubules into the peritubular capillaries.: That describes reabsorption, the opposite of secretion.
B. Tubular secretion is a passive process that occurs in the glomerulus, allowing the filtration of waste products.: Filtration in the glomerulus is a separate, largely passive process; tubular secretion is an active transport process occurring in the renal tubules.
C. Tubular secretion is the movement of substances from the blood in the peritubular capillaries into the renal tubules.: This correctly describes tubular secretion (e.g., H⁺, K⁺, drugs) .
D. Tubular secretion primarily occurs in the Bowman's capsule, facilitating the selective reabsorption of essential nutrients.: Bowman's capsule is the site of filtration, not tubular secretion; selective reabsorption occurs later in the tubules.