gwd29-40

pianer

我想请ＮＮ们帮我分析以下这题：
Q40:
Mice that have been given morphine are very likely to develop blood poisoning because bacteria that normally reside in the intestine typically respond to morphine by migrating into the bloodstream.  However, when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent, although it does still occur.  These results provide support for researchers’ prediction that naltrexone will turn out to be toxic to certain types of bacteria.
 

Which of the following, if discovered to be true, would most seriously weaken the support for the researchers’ prediction?
 

After being administered to mice, naltrexone does not pass from the bloodstream into the intestine. Naltrexone inhibits morphine from triggering the migration of intestinal bacteria into the bloodstream. Mice that have been given naltrexone but not morphine have no greater risk of developing blood poisoning than do mice that have not been given either substance. The increased risk of blood poisoning is not the only harmful effect on mice of being given morphine. Conditions other than the presence of intestinal bacteria in the bloodstream can cause blood poisoning in mice.    Answer: Ｅ　　ＷＨＹ？

yoyo9012

My version says B is the answer. Here is my analysis:

        

The situation:

        

            
1. Morphine
        è
        bacteria migrate to blood stream è
        blood poisoning
               
2. Morohine
        + naltrexine è less frequent blood
        poisoning
           

        

è Prediction: Naltrexone
is toxic to some bacteria

        

To weaken the SUPPORT of the prediction (i.e. weaken (2)),
we must show that the less frequent blood poisoning is not because naltrexone
kills bacteria, but rather did something else. (such that the evidence can no
longer be used as support for the prediction.)

        

            
1. even
        if naltrexone does not get into intestine, it can still kill bacteria in
        the blood stream, after the bacteria are triggered by morphine to migrate
        to the blood stream.
               
2. Correct.
        This statement shows that naltrexone inhibits bacteria from causing blood
        poisoning by preventing them from migrating into the blood stream, a step
        earlier than that the researcher predicted. Therefore, the observed less
        frequent blood poisoning cannot support the prediction.
               
3. Mice
        that receive only naltrexone and those that receive none of the drugs are similarly
        unlikely to get blood poisoning. Because neither group of mice receive
        morphine, whether naltrexone kills bacteria is not important.
               
4. It may
        be true that morphine can cause additional side effects on mice. But it is
        only the bllod poisoning that we are interested in here. This statement is
        irrelevant.
   

pite82

这里顺便说一句：这题的要求是weaken support for the prediction，而不是weaken the prediction. 所以就要说明第二个实验不能证明科学家的观点。所以不是断桥就是他因。

mandying

M会导致B进入血管，从而血液中毒；但是当M+N时，血液中毒少啦。推出N会导致B减少进入血管

Weaken support:N阻碍M去引起B进入血管

huarenhong

我也选B, E把原题中

Morphine è bacteria migrate to blood stream －〉blood poisoning 的逻辑之外又加上一种

Conditions other than the presence of intestinal bacteria in the bloodstream－〉blood poisoning 的情况，毫不相关

jasnoyang

就如楼上提醒的，weaken support和weaken prediction 不同。

那这个support是什么呢？为了预测M is toxic to BAC的性能而做的一组实验，Weaken the support 的实质就是质疑实验设计的合理性。我们知道一个实验最好排除一个待研究因素之外的所有因素，其结果才好解释。如果这个实验除了要研究的因素之外还有第二个因素，那么仅仅改变第一个因素而没有限定第二个因素，是没有办法得出的结论的。

B说明实验设计本身没有问题，也就是其结果能解释M的作用机制，虽然其结果实际上就是否定了Prediction，但是没有Weaken support本身。

而E从头否定了实验的意义-----即那一组实验设计没有排除其他因素，其结果没有唯一解释----因此既不存在支持Prediction，也不能否定Prediction --- 从而那个实验是白忙呼 -- weakens the support

欢迎拍砖！

pianer

谢谢，之前没注意到这个细节差别。