Maize contains the vitamin niacin, but not in a form the body can absorb. Pellagra is a disease that results from niacin deficiency. When maize was introduced into southern Europe from the Americas in the eighteenth century, it quickly became a dietary staple, and many Europeans who came to subsist primarily on maize developed pellagra. Pellagra was virtually unknown at that time in the Americas, however, even among people who subsisted primarily on maize.

Which of the following, if true, most helps to explain the contrasting incidence of pellagra described above?

Once introduced into southern Europe, maize became popular with landowners because of its high yields relative to other cereal crops.Maize grown in the Americas contained more niacin than maize grown in Europe did.Traditional ways of preparing maize in the Americas convert maize’s niacin into a nutritionally useful form. In southern Europe many of the people who consumed maize also ate niacin-rich foods.Before the discovery of pellagra’s link with niacin, it was widely believed that the disease was an infection that could be transmitted from person to person.

答案是C。我怎么始终看不明白这题是什么意思啊？论坛上也搜不到这题的讨论,是不是太简单了? 请各位XDJM给点思路。

题目要解释为什么European和American都吃maize，为什么E得病，而A不得病。

前提提到得P病的原因是n的不足，而n不足是因为m里面的n不可以吸收。因此可以推出如果n可以吸收的话，那么就不会有P了。

C就解释了用传统方法做m，n就可以吸收，所以A就没有病了。同时暗含E没有用传统方法做m。

A：对原文复述，无用

B：不能解释A和E本质的不同

C：通过传统方法将N转化成营养的、有用的形式，从而解释E得病上升的原因

D：如果D是真的，那么结论将是E的人也不会得病，或者至少得病者不会上升

E：如果E是真的， 那么因为人们害怕被传染，一旦发现糙皮病，人们避之不及，既然widely believed,那么肯定有健全的隔离政策，得病的人数量应该会被控制，不能解释得病增加