Question ID:PT79 S1 Q21 Passage:People with higher-than-average blood levels of a normal dietary by-product called homocysteine are twice as likely to be diagnosed with Alzheimer's disease as are those with average or below-average homocysteine levels. Thus, it is likely that the risk of developing Alzheimer's disease could be reduced by including in one's diet large amounts of B vitamins and folic acid, which convert homocysteine into substances known to have no relation to Alzheimer's disease. Stem:Which one of the following, if true, most seriously weakens the argument? Correct Answer Choice:EChoice A:Many Alzheimer's patients have normal homocysteine levels. Choice B:The substances into which homocysteine is converted can sometimes have harmful effects unrelated to Alzheimer's disease. Choice C:B vitamins and folic acid are not metabolized by the body very efficiently when taken in the form of vitamin-mineral supplements. Choice D:People whose relatives contracted Alzheimer's disease are much more likely to develop Alzheimer's than those whose relatives did not. Choice E:Alzheimer's disease tends to increase the levels of homocysteine in the blood.