某6个月女婴，母乳喂养未添加辅食，面色苍黄、嗜睡，诊断为巨幼细胞贫血，其主要原因是缺乏
A．蛋白质
B．铁
C．维生素A
D．维生素B2
E．维生素B12
参考答案：E
解析： 巨幼细胞贫血的发生主要是一碳单位代谢的障碍引起的。由于体内缺乏维生素B12，转甲基酶催化的同型半胱氨酸转变为蛋氨酸的反应受阻，N5甲基四氢叶酸的甲基不能转移出去，组织中的游离四氢叶酸减少，导致核酸合成障碍，影响细胞分裂，引起巨幼细胞贫血。故E项符合。
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| One day I go to my good friend Bruce's home. There are four people in his family. His parents 1 both English teachers. He 2 a little brother. 3 name is Peter. Peter is only five years old. He doesn't 4 to school. So he doesn't know how to read or write. I see Peter sitting at the table with a pen 5 his hand."What are you doing, Peter?" I ask."I'm writing 6 my friend, Bill." says Peter."But how 7 write?" asks Bruce."You don't know the words, because (因为) you don't go to 8 ". With a smile, Peter says."But it doesn't matter (没关 系)because my 9 and I know the words on the moon. I write to him in the moon language. It's easy (容易 的) for him to read my letter. I tell him an interesting story. I'm sure Bill will be 10 to read it." What an interesting answer it is! | ||||
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