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题目材料：
When blood samples from elderly people were tested for levels of vitamin B12, it was found that those whose blood was deficient in B12 were four times more likely than were other elderly people to have symptoms characteristic of the early stages of Alzheimer's disease, such as increasing forgetfulness. Clearly, therefore, either a diet low in B12 disposes a person to Alzheimer's disease, or Alzheimer's disease affects the absorption of dietary B12 into the blood.
Which of the following, if true, most seriously weakens the argument?
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APeople in the early stages of Alzheimer's disease often neglect maintaining a healthy diet.
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BMost of those who develop Alzheimer's disease do not exhibit any symptoms of the disease before the age of 60.
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CMany people who are in the early stages of Alzheimer's disease are not aware that they have it.
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DMany young people have diets that are deficient in vitamin B12.
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EDeficiencies in B vitamins other than B12 are not as strongly correlated with Alzheimer's disease as is vitamin B12 deficiency.
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