@Crystal the conclusion here is, "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 support? "Rhizobium bacteria living in the roots of bean plants or other legumes produced 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."
But just because Rhizobium bacteria living in the roots of bean plants or other legumes produce fixed nitrogen, it doesn't necessarily mean that Rhizobium bacteria living in the roots of non-legume crops, such as wheat, will also produce fixed nitrogen.
This is a Strengthen with Necessary Premise question so we are looking for the answer choice that not only strengthens the argument but that is also required for the argument.
(E) clearly strengthens the argument by stating, "Rhizobium bacteria living in the roots of wheat would produce fixed nitrogen."
Now let's negate (E) and see if it causes the argument to fall apart. The negation of (E) is, "Rhizobium bacteria living in the roots of wheat would not produce fixed nitrogen."
This clearly destroys the conclusion so (E) is the correct answer.
(B) also strengthens the argument but the problem with (B) is that it is not required for the argument.
The negation of (B) would be, "Fixed nitrogen is not necessarily the only soil nutrient that must be supplied by artificial fertilizer for growing wheat crops."
Okay fine, but even if fixed nitrogen is one of other soil nutrients, figuring out a way to produce nitrogen naturally would still REDUCE the need for artificial fertilizers.
Notice the conclusion here is not that the need for artificial fertilizers will be completely eliminated.
Hope this helps! Please let us know if you have any other questions.
