--Situation: 1)M contains n, not in a form the body can absorb。 2)n Deficiency causes P. 3)M was introduced to Europe from US and then became the main food of European, making some European get P. 4)P was not known in US. at that time,even in people subsist on M. --Reason: Someting makes US. people avoid n deficiency when they eat M, while European didnt encounter that thing. SO。。。。 C。
[此贴子已经被作者于2007-9-22 22:59:18编辑过] |