1.Half of the subjects in an experiment—the experimental group—consumed large quantities of a popular artificial sweetener. Afterward, this group showed lower cognitive abilities than did the other half of the subjects—the control group—who did not consume the sweetener. The detrimental effects were attributed to an amino acid that is one of the sweetener’s principal constituents.
Which of the following, if true, would best help explain how the sweetener might produce the observed effect?
(A) The government’s analysis of the artificial sweetener determined that it was sold in relatively pure form.
(B) A high level of the amino acid in the blood inhibits the synthesis of a substance required for normal brain functioning.
(C) Because the sweetener is used primarily as a food additive, adverse reactions to it are rarely noticed by consumers.
(D) The amino acid that is a constituent of the sweetener is also sold separately as a dietary supplement.
(E) Subjects in the experiment did not know whether they were consuming the sweetener or a second, harmless substance.
2. Adult female rats who have never before encountered rat pups will start to show maternal behaviors after being confined with a pup for about seven days. This period can be considerably shortened by disabling the female’s sense of smell or by removing the scent-producing glands of the pup.
Which of the following hypotheses best explains the contrast described above?
(A) The sense of smell in adult female rats is more acute than that in rat pups.
(B) The amount of scent produced by rat pups increases when they are in the presence of a female rat that did not bear them.
(C) Female rats that have given birth are more affected by olfactory cues than are female rats that have never given birth.
(D) A female rat that has given birth shows maternal behavior toward rat pups that she did not bear more quickly than does a female rat that has never given birth.
(E) The development of a female rat's maternal interest in a rat pup that she did not bear is inhibited by the odor of the pup.
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