This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'If urine sample darkens on standing, the most likely condition is : \nSelect and explain. \nA. Phenylketonuria, B. Alkaptonuria, C. Maple syrup disease, D. Tyrosinemia', 'role': 'user'}, {'content': "Answer: B \nExplanation: Alkaptonuria a condition d/t defective homogentisate 1, 2- dioxygenase (1/t defective tyrosine degradation) usually presents after age of 40 with characteristic triad of Homogentisic aciduria (which blacken/darkens on exposure to air /standing and is strongly Benedict's positive), Ochronosis (i.e black pigmentation of cailage & collagenous connective tissue), and Ahritis of large joints", 'role': 'assistant'}]