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原文相关段落：
We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood tryptophan level and the
concentrations of tryptophan and of serotonin in the brain increased after the meal.
Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell. Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan.
86. It can be inferred from the passage that the authors initially held which of the
following hypotheses about what would happen when they fed large amounts of
protein to rats?
(A) The rats’ brain serotonin levels would not decrease.
(B) The rats’ brain tryptophan levels would decrease.
(C) The rats’ tyrosine levels would increase less quickly than would their
leucine levels.
(D) The rats would produce more insulin.
(E) The rats would produce neurotransmitters other than serotonin.
纠结AB选项啊，“As we had hypothesized, the blood tryptophan level and the concentrations of tryptophan and of serotonin in the brain increased after the meal” 根据这句话 不应该选B嘛？ |
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发表于 2016-3-30 00:03:55
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