Although migraine headaches are believed to be caused by food allergies, putting patients on diets that eliminate those foods to which the patients have been damonstrated to have allergic migraine reactions frequently does not stop deadaches. Obviously, some other cause of migraine headaches besides food allergies must exist.

Which of the following, if true, would most weaken the conclusion above?

A.many common foods elicit an allergic response only after several days, making it very difficult to observe links between specific foods patients eat and headaches they develop.

B.Food allergies affect many people who never develop the symptom of migraine headaches.

C. Many patients report that the foods that cause them migraine headaches are amongthe foods that they most enjoy eating.

D.very few patients have allergic migraine reactions as children and then live migraine-free adult lives once they have eliminated from their diets foods to which they have been demonstrated to be allergic.

E.very rarely do food allergies cause patients to suffer a symptom more severe than that of migraine headaches.

答案 是A。但A说通常食物要在几天后才有中毒表现，导致要将食物中毒病人和由食物中毒导致的头痛联系起来相当困难。即是讲 食物中毒-->几天后才中毒表现，则表明在发生头痛的前几天肯定是食物以外的因素导致的头痛，那就是支持了原文结论，怎么会是weaken呢？请nns指点。