单选题 9. When rats are placed under conditions of stress, their adrenal glands immediately increase production of the hormone corticosterone, and soon thereafter the rats' white blood cell count drops substantially. Yet rats without functioning adrenal glands experience little decrease in white blood cell count when placed under conditions of stress. It is likely, therefore, that an increase in corticosterone produced by a rat's adrenal glands causes the rat's white blood cell count to decrease.
Which of the following would it be most useful to know in evaluating the reasoning of the argument? ______

A、 Whether the drop in white blood cell count that occurs in rats under conditions of stress is sufficient to make the rats more susceptible to diseases that white blood cells normally combat
B、 Whether normal white blood cell counts vary widely among healthy rats that are not under conditions of stress
C、 Whether the adrenal glands of rats that are under conditions of stress increase production of any hormone other than corticosterone
D、 Whether the adrenal glands of rats produce elevated levels of corticosterone on occasions when the rats are not under conditions of stress
E、 Whether rats' adrenal glands are affected by hormones produced by any of the rats' other organs.

【正确答案】 C

【答案解析】 C：Yes：皮质酮增加了，其他激素也增加→有可能是其他激素导致白细胞数量下降，寻找他因，削弱原文；No：只有皮质酮增加→只能是皮质酮导致白细胞数量下降，排除他因，加强原文。正确。
A：“疾病”属于无关信息，不选。
B：“健康老鼠”属于无关信息，不选。
D：文章最终的结论针对的是处于应激状态的老鼠，而非不处于应激状态的老鼠。
E：肾上腺受到的影响和本文没关系，不选。