2011年GMAT考试阅读材料38(附答案)(3)

　　(D) Meals that had very low concentrations of tyrosine

　　(E) Meals that had very low concentrations of leucine

　　9. 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.

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