This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal tract, Subject name: Pediatrics
A two year old child presents with persistent diarrhaea acidic stools and presence of one per cent of reducing substance in the fresh stools. What is the most probable diagnosis ? 
Select and explain. 
A. Cystic fibrosis, B. Lactose intolerance, C. Rotavirus induced diarrhoea, D. Intestinal tuberculosis
B: Lactose intolerance
Answer: B: Lactose intolerance 
Explanation: DISACCHARIDASES DEFECIENCY Lactase defeciency diagnosis based on presence of more than .5%of reducing substance in the fresh stools acidic stools abnormal oral sugar tolerance test breath Hydrogen excretion of more than 11ppm following a loading dose of lactose enzyme assay on mucosal biopsies showing low levels of disaccharidases Ref : ESSENTIAL PEDIATRICS,O.P.GHAI,PG NO:274, 7th edition