GWD-24-35

yujunchening

The milk of many mammals contains cannabinoids, substances that are known to stimulate certain receptors in the brain. To investigate the function of cannabinoids, researchers injected newborn mice with a chemical that is known to block cannabinoides from reaching their receptors in the brain. The injected mice showed far less interest in feeding than normal newborn mice do. Therefore, cannabinoids probably function to stimulate the appetite.

Which of the following is an assumption on which the argument depends?

A.Newborn mice do not normally ingest any substance other than their mothers’ milk.

B.Cannabinoids are the only substances in mammals’ milk that stimulate the appetite.

C.The mothers of newborn mice do not normally make any effort to encourage their babies to feed.

D.The milk of mammals would be less nutritious if it did not contain cannabinoids.

E.The chemical that blocks cannabinoids from stimulating their brain receptors does not independently inhibit the appetite.

想问一下为什么选B不对呢？

reirayanqing

即使Cannabinoids are the only substances in mammals’ milk that

stimulate the appetite成立
如果the substance ejected into the mice 抑制appetite，那么也会有题

目中提到的结果。

也就是说你要验证一个变量A的作用，却引入了另外一个变量B，是不科学的

（这样无法确认是谁的作用了）
要使用控制变量法

sherilynchi

不明白。。哪位高人再给解答一下下。

jasper123

这种假设题通常都是要排除他因，你要证明老鼠的食欲减退就是因为C没到达receptors引起的，没有别的原因，才能形成推出这句（cannabinoids probably function to stimulate the appetite.)结论的必要条件。

如果说注射的那种化学物质本身就能抑制食欲的话，就没法证明食欲减退是因为大脑受体没接触到C，也就退不出结论了。
排除他因通常都是否定句哦~~还有就是，B项里的only这种极端词一般不选，除非结论里也有极端词......

yujunchening

看懂了 thanks!