【单选题】
人体内维生素D的生理活性形式为?
①
25-(OH)-D3
②
24，25-(OH)2-D3
③
25-(OH)-D2
④
1，25-(OH)2-D3 1，25-(OH)2-D2
【单选题】
佝偻病的发生是由于缺乏（ ）．
①
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②
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③
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④
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