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. Which one of the following, if true, most seriously weakens the argument?
A: Alzheimer's disease tends to increase the levels of homocysteine in the blood.
B: Many Alzheimer's patients have normal homocysteine levels.
C: B vitamins and folic acid are not metabolized by the body very efficiently when taken in the form of vitamin-mineral supplements.
D: People whose relatives contracted Alzheimer's disease are much more likely to develop Alzheimer's than those whose relatives did not.
Choose A, B, C or D as your solution.
A