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 America 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 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?

　　(A) Once introduced into southern Europe, maize became popular with landowners because of its high yields relative to other cereal crops.

　　(B) Maize grown in the Americas contained more niacin than maize grown in Europe did.

　　(C) Traditional ways of preparing maize in the Americas convert maize’s niacin into a nutritionally useful form.

　　(D) In southern Europe many of the people who consumed maize also ate niacin-rich foods.

　　(E) 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.

　　翻译：

　　玉米中含有一种维生素烟酸，但它在玉米中的构成形式是人体不可吸收的。糙皮病是一种因缺乏烟酸导致的疾病。18世纪时，当玉米从美洲引入到欧洲南部后，它迅速成为主食，许多主要吃玉米的欧洲人来得了糙皮病。然而，当时在美洲，即使是在主要吃玉米的人当中，糙皮病其实都还是未知的。

　　下列哪项，如果为真时，最有助于解释如上所述中糙皮病的不同发病率呢?

　　(A) 玉米被介绍到欧洲南部后成为地主当中流行的食物，因为其相对其他谷物产量高。

　　(B) 在美洲种植的玉米比在欧洲种植的玉米含有较多的烟酸。

　　(C) 在美洲，烹调玉米的传统方式将玉米中的烟酸转换成营养可用的形式。

　　(D) 在欧洲南部的许多吃玉米的人也吃烟酸丰富的食物。

　　(E) 发现糙皮病与烟酸有关之前，它被广泛认为是可以从人到人传播感染的。