单选题：WhatdoweknowaboutNAD?

题目内容：

WhatdoweknowaboutNAD? A．Itisanartificialcompound.
B．Itismadeofyoungcells.
C．Itcanreviveoldercells.
D．Itcanbemadeinoneweek.

参考答案：

答案解析：

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