This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Beta thalasemmia, Subject name: Pathology
[{'content': "Hydrops fetalis d/t Hb ba is associated with? \nSelect and explain. \nA. Hb ba's cannot bind oxygen, B. The excess alpha-globin form insoluble precipitates, C. Hb ba's cannot release oxygen to fetal tissues, D. Microcytic red cells become tapped in the placenta", 'role': 'user'}, {'content': 'Answer: C \nExplanation: - Hydrops fetalis is seen in most severe form of a-thalassemia, caused by deletion of all four a-globin genes. - Hb in these fetus have tetramers of g-globin chains (hemoglobin Bas) which have high affinity for oxygen. - This results in decreased delivery of oxygen to the tissues. - Survival in early development of these fetus is d/t expression of z chains, an embryonic globin that pairs with g chains to form functional z 2 g 2 Hb tetramer.', 'role': 'assistant'}]