Which of the following substances triggers a hypersensitivity reaction?

a. Kidneys: Kidney dysfunction can affect waste elimination and fluid balance but does not typically cause yellow sclera.

b. Appendix: The appendix is involved in the immune response and gut flora regulation but not in causing yellow sclera.

c. Liver: Liver dysfunction can lead to jaundice, where bilirubin accumulates in the blood and tissues, causing yellowing of the skin and sclera.

d. Spleen: The spleen is involved in blood filtration and immune response but does not directly cause yellow sclera

a. Secretes fluid to reduce friction between layers: This is correct. The pleural membranes secrete pleural fluid, which reduces friction between the visceral and parietal layers during breathing.

b. Secretes a substance that reduces surface tension of alveoli: This describes the function of surfactant, which is secreted by alveolar cells, not pleural membranes.

c. Secretes a substance to keep epithelial cells wet: This is a general description that doesn't specifically apply to pleural membranes.

d. Secretes fluid involved in protection from infections: While pleural fluid may have some protective roles, its primary function is to reduce friction, not directly to protect from infections.