Rhizobium bacteria living in the roots of bean plants or other legumes produce fixed nitrogen, which is one of the es...

Ravi on January 15, 2020

@Jacinta-Onu,

Great question. Let's look at (B) and (E).

This is a strengthen with a necessary premise question. We can use the
negation test to test each answer choice. The correct answer, when
negated, will wreck the argument. When the negation wrecks the
argument, this shows that the answer choice in its original form is
required for the argument to make any sense.

(B) says, "Fixed nitrogen is currently the only soil nutrient that
must be supplied by artificial fertilizer for growing wheat crops."

(B)'s negation would say, "Fixed nitrogen is not currently the only
soil nutrient that must be supplied by artificial fertilizer for
growing wheat crops."

(B)'s negation doesn't wreck the argument because the original
statement is so strong. It's true that (B) does strengthen the
argument because if there are other nutrients contained in the
fertilizer, then it's possible that even if we solve the nitrogen
problem, we would have to keep on using the fertilizers. However, it's
still not necessary to make this conclusion because it's still
possible to reach the conclusion even if there were currently other
nutrients in the fertilizer. It's possible that we'd be able to supply
those nutrients in other types of ways in the future, and because the
conclusion is based on the hypothetical of succeeding in producing
Rhizobium in wheat plants, the future isn't off-limits. Thus, (B) can
be eliminated from contention.

(E) says, "Rhizobium bacteria living in the roots of wheat would
produce fixed nitrogen."

(E)'s negation would say, "Rhizobium bacteria living in the roots of
wheat would not produce fixed nitrogen."

It's the fixed nitrogen that fertilizes the crops. If the bacteria
don't produce this in the wheat crop (which is what the negation of
(E) says,), then it will not fertilize and will not work. Thus, (E)'s
negation wrecks the argument, so (E) is the correct answer choice and
is a necessary premise.

Does this make sense? Let us know if you have any other questions!