In the human body, the action of surfactant is done by-

Ans. is 'c' i.e lipid and protein Approximate composition of a surfactantComponentPercentage compositionDipalmitoyl Phosphatidylcholine(DPPC)62Phosphatidylglycerol*5Other phospholipids10Neutral lipids13Proteins8Carbohydrate2DPPC and PG are types of phospholipids.Thus surfactant is made up of lipids and protein (and carbohydrate).Surfactant action by a molecule requires it to be amphipathic i.e. it should have both a polar group and a non polar chain; such a combination is possessed by lipids (phospholipids) & proteins.