请教一个题的思路

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. 

我选了C， 感觉好像是手段可以达到目的的解题方法， 但是答案是E 很是不理解， 觉得E 是题目里给出来的条件。 

请大家帮我扭转一下我的思路， 谢谢

试下...

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,(手段) the need for artificial fertilizers will be reduced. (目的)

标志IF 手段达到目的题.

The argument above makes which one of the following assumptions?
   假设-->方法:取非削弱,削弱:手段不可行

(A) Biotechnology should NOT be directed toward producing plants that do not require artificial fertilize. -->无关

(B) Fixed nitrogen is NOT currently the only soil nutrient that must be supplied by artificial fertilizer for growing wheat crops.  ->ONLY绝对化字眼....且加NOT后不削弱结论

(C) There are no naturally occurring strains of wheat or other grasses that have Rhizobium bacteria living in their roots.---->加强不等于假设,NO去掉,看是否削弱,小麦本来根部有RB,也就不用化肥---和结论一致,所以加NOT后没有削弱结论,否定前提, 没有证明手段不可行,且OTHER GRASSES转移讨论区域

(D) Legumes are NOT currently the only corps that produce their own supply of fixed nitrogen. --->ONLY绝对化,且加NOT后加强

(E) Rhizobium bacteria living in the roots of wheat would NOT produce fixed nitrogen. --->加NOT后削弱...RB在小麦的根部不会产生FN,biotechnology 成功在 wheat strains的根部让Rhizobium bacteria生长也不会产生FN,还是需要化肥,削弱了结论,所以选E