This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Which disaccharides are not broken down in git? 
Select and explain. 
A. Lactulose, B. Maltose, C. Sucrose, D. Lactose
A: Lactulose
Answer: A: Lactulose 
Explanation: LactuloseComposition: O-a-d-galactopyranosyl-(1-4)-b-d-fructofuranoseSource: Heated milk (small amounts), mainly syntheticClinical Significance: Not hydrolyzed by intestinal enzymes, but fermented by intestinal bacteria; used as a mild osmotic laxativeFermentation of lactulose results in acidification of the gut contents so that ammonia produced by intestinal bacteria is trapped as ammonium that cannot diffuse into the bloodstream.Fermentation of lactulose results in an eightfold increase in the osmolality of the gut contents so that there is more water for ammonia and ammonium to dissolve in so that less is absorbed into the bloodstream.Ref: Harper&;s Biochemistry, 30th edition, page no: 170, table 15-4