Option (4) is the correct answer because digestion of polysaccharides like starch occurs in mouth and digestion of disaccharides occurs in small intestine. Option (3) is incorrect because saliva contains mucus which helps in the lubrication of oral cavity. Option (1) is incorrect because saliva contains an antibacterial agent-lysozyme so that it controls bacterial population in mouth. Option (2) is incorrect because digestion of complex carbohydrates are performed by secretions from salivary glands.