This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nucleotides, Subject name: Biochemistry
[{'content': 'Deficiency of which of the following enzyme leads to toxicity of 5-fluorouracil? \nSelect and explain. \nA. Purine nucleoside phosphorylase, B. Dihydropyrimidine dehydrogenase, C. PRPP synthase, D. Adenosine deaminase', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 5-fluorouracil is acted upon by dihydropyrimidine dehydrogenase - Deficiency - accumulation of 5-FU - toxicity.', 'role': 'assistant'}]