求教FeiFei-89-->babypace转移

I do not agree with enhance's explaination. I think the B answer must be right too!  

主要问题就出在ONLY这个词上，并没有这个意思

R细菌能提供N，并不以别的菌不能提供N为前提啊。

还是不太明白呀

为什么对B取非,不能削弱结论呢?如果,对B取非,即:Fixed nitrogen 并不是 artificial fertilizer 提供的唯一nutrient,这样的话,artificial fertilizer 还有可能提供对WHEAT生长有利的其他NUTRIENT.如果这样,the need for artificial fertilizers 也不一定会reduced,这不就是削弱了结论吗?

而且,ONLY这个词不一定是要从文中推出呀,第79题,文中也没有说ONLY,但答案E中也一样有ONLY呀?这说明ONLY在ASSUMPTION起的是否定其他因素的作用.

N 79. Despite improvements in treatment for asthma, the death rate from this disease has doubled during the past decade from its previous rate. Two possible explanations for this increase have been offered. First, the recording of deaths due to asthma has become more widespread and accurate in the past decade than it had been previously. Second, there has been an increase in urban pollution. However, since the rate of deaths due to asthma has increased dramatically even in cities with long-standing, comprehensive medical records and with little or no urban pollution, one must instead conclude that the cause of increased deaths is the use of bronchial inhalers by asthma sufferers to relieve their symptoms.

89. Rhizobium bacteria living in the roots of bean plants or other legumes produce fixed nitrogen, which is one of the essential plant nutrients and which for non-legume crops, such as wheat, normally must be supplied by applications of nitrogen-based fertilizer. So if biotechnology succeeds in producing wheat strains whose roots will play host to Rhizobium bacteria, the need for artificial fertilizers will be reduced.
The argument above makes which one of the following assumptions?
(A) Biotechnology should be directed toward producing plants that do not require artificial fertilize.
(B) Fixed nitrogen is currently the only soil nutrient that must be supplied by artificial fertilizer for growing wheat crops.
(C) There are no naturally occurring strains of wheat or other grasses that have Rhizobium bacteria living in their roots.
(D) Legumes are currently the only corps that produce their own supply of fixed nitrogen.
(E) Rhizobium bacteria living in the roots of wheat would produce fixed nitrogen.

让我尝试一下：E是消除了文中的GAP,原因前人已经或明。

而B取非就是说Fixed nitrogen不是人工肥料必须要共给wheat crops的唯一的营养。并不能反对结论说：人工肥料的需求会减少（就算人工肥料还提供其它的营养，bateria提供nitrogen，也是可以减少人工肥料的用量的）。它反对的是：有了bateria以后不需要再用人工肥料！

不知道我说得对不对。

cicilla is right.

I carelessly mistook "reduced" for " removed" , then I choose B.

The reason is just what cicilla has said.

Be careful on every words.