This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: parasitology, Subject name: Microbiology
[{'content': 'A pregnant woman is able to transfer oxygen to her fetus because fetal hemoglobin has a greater affinity for oxygen than does adult hemoglobin. Why is the affinity of fetal hemoglobin for oxygen higher \nSelect and explain. \nA. The oxygen-binding curve of fetal hemoglobin is shifted to the right., B. Fetal hemoglobin binds 2,3-BPG with fewer ionic bonds than the adult form., C. There is less 2,3-BPG in the fetal circulation as compared to maternal circulation, D. The tense form of hemoglobin is more prevalent in the circulation of the fetus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In adult hemoglobin 2,3-BPG binds to ionized residues in the interface between the two b-chains, thus decreasing the oxygen affinity. The g-chains of fetal hemoglobin have fewer ionized residues in the corresponding interface and bind 2,3-BPG with less affinity, which allows for a greater binding affinity for oxygen. Ref:- Lippincott textbook of Biochemistry', 'role': 'assistant'}]