单选题 27. In an experiment, a group of pregnant mice were each given food containing minute doses of the hormone BPA. A control group of pregnant mice were given no BPA. Offspring of mothers that had been given BPA were 10 percent bigger when weaned from their mothers than were offspring of mothers in the control group. Clearly, this result supports the hypothesis that the physical development of mice is significantly affected by prenatal exposure to BPA.
Which of the following is an assumption on which the argument depends? ______

A、 Prenatal exposure of mice to doses of BPA even smaller than those used in the experiment would not have significantly affected the physical development of the mice.
B、 At birth, there was no difference in size between offspring of mothers that had been given BPA and offspring of mothers in the control group.
C、 Postnatal exposure of mice to BPA before the mice are weaned has significant effects on the physical development of the mice.
D、 Exposure of a pregnant mouse to the doses of BPA used in the experiment does not significantly enhance its ability to nurse its offspring.
E、 Significant differences in size between offspring of mothers that had been given BPA and offspring of mothers in the control group persisted long after the offspring were weaned

【正确答案】 B

【答案解析】 B：选项取反。大小不同→不是因为BPA，而是因为生下来的时候身体大小就不一样，削弱原文，正确。
A：和剂量无关。
C：产后接触BPA不是本文讨论的内容。
D：本文讨论的是老鼠产前接触BPA对其发育的影响，而该选项讨论的喂奶行为已经是产后了，无关。
E：文章讨论的是断奶时老鼠的大小，和断奶后很久无关。