The question stem says, the argument relies on the assumption that blank, so this is a necessary assumption question.

Let's go ahead and break down this argument and then think about what the argument must assume in order for it to make sense.

led the farmers in a certain region to abandon the practice of periodically growing a green manure crop,

such as alfalfa, which is an example of a green manure crop.

And the reason farmers used to grow green manure crops was to rejuvenate the soil.

So in the past, farmers used to grow green manure crop to help improve soil quality,

but then chemical fertilizers were introduced, and it was just like the introduction of rock music, it corrupted the youth.

Chemical fertilizers corrupted farmers. They no longer wanted to grow green manure crops.

After the introduction of chemical fertilizers, they no longer grow green manure crops.

This is the timeline of events. In the past, chemical fertilizers came along, now they don't grow green manure crops.

Now as a result, the soil structure in a typical farm field in the region is poor.

So because these farmers no longer grow green manure crops, that caused the soil in the region to be poor.

Now based on that, the author reaches the following conclusion here.

So, to significantly improve the soil structure, farmers will need to abandon the use of chemical fertilizers.

If we want to make sure that the soil is no longer poor, we have to get rid of the chemical fertilizers,

we can't use them anymore, is what the author is saying.

Now we know that there must be something flawed about reaching this conclusion because it's a necessary assumption question.

So can you think about why, even though the premises are true,

it does not have to be true that farmers will need to abandon the use of chemical fertilizers to significantly improve soil structure?

Is there some way that farmers actually could continue to use chemical fertilizers, but still be able to improve soil structure?

That's what we should be thinking about.

And the question that I have right now is, well, why can't we just get the farmers to grow green manure crops again?

If green manure crops were the thing that was helping to keep the soil healthier in the past,

what's stopping us from educating the farmers and saying, hey, the green poop crops, they were really good.

Start growing them again.

Why can't we just both use chemical fertilizers and grow green manure crops at the same time?

The author has not given us any evidence that we cannot do both of these things at the same time.

Now, it is true that what happened is that farmers stopped growing green manure crops when chemical fertilizers came around,

but that's just something that happened.

That doesn't have to happen again in the future.

There's nothing like physically stopping farmers from growing green manure crops, right?

So in order to make this argument, in order to reach this conclusion,

the author has to assume that the farmers will not grow green manure crops unless we abandon chemical fertilizers.

Now, in case it helps, I'm going to be even more technical with this explanation now,

if you're having a hard time understanding the earlier explanation.

Technically, what happened here is that the premises established certain causal relationships that did occur in the past.

So the introduction of chemical fertilizers, it did cause farmers to stop growing green manure,

and then this did cause poor soil.

But the author is actually making multiple assumptions to get from this chain of causal relationships to the conclusion.

What the author is assuming is that these are essentially conditional relationships.

The author is thinking that if people are using chemical fertilizer,

then that guarantees that they will never grow green manure.

So this straight arrow here, this is a conditional arrow as opposed to this one-time causal arrow.

The author is turning this one-time causal relationship that we observed in history

into a conditional that is just holding and forever true.

And then technically, the author is also turning this causal claim into a conditional.

They are assuming that if you don't grow green manure, sorry, that should have been a slash before,

that if you don't grow green manure, then that guarantees you will have poor soil.

This is why the author thinks in the conclusion that if you don't want to have poor soil anymore,

if you want to avoid poor soil, what the author is thinking is you have to grow green manure,

which the author thinks means you have to stop using chemical fertilizer.

This is the assumption the author is making, which is why they think if you want to avoid poor soil,

you have to not use chemical fertilizer.

But all of this is an assumption.

The premises did not establish that chemical fertilizers guarantee all the time not growing green manure.

And actually, the premises did not establish that if you don't grow green manure,

you are guaranteed to have poor soil.

Sure, this one-time, this did happen in the area,

but that doesn't mean as long as you stop growing green manure, you are always bound to have poor soil.

So if we can understand the argument in this way,

then when we go to these answers, we actually can tell the answer is either going to sound something like

The author is assuming that if you grow chemical fertilizers,

then you won't grow green manure, or the contrapositive of that relationship.

Or the answer might say, if you don't grow green manure,

then you will always have poor soil, or the contrapositive of that relationship.

Now let me start with the answer choices B and C, and then I'll turn to the other three.

Applying chemical fertilizers to green manure crops, such as alfalfa,

has no positive effect on their growth?

Now this isn't necessary because the argument's logic did not depend

on some causal relationship between chemical fertilizers

and the quality of the growth of the green manure.

Now it is true that the author is assuming that if farmers are using chemical fertilizers,

the farmers will not choose to grow green manure,

but that does not imply that the chemical fertilizers,

if they were applied to green manure crops, wouldn't help them grow at all.

Maybe the chemical fertilizers actually would help the green manure crops grow,

it's just that the farmers are choosing not to grow the green manure crops.

So that's why B is not necessary.

The issue is about what the farmers are choosing to do.

It's not about the actual effect of the fertilizer on the plant's growth itself.

It's about the farmer's choice to grow.

That's why B is not necessary.

is soil structure.

Well there's nothing here to suggest what is the number one,

most important, absolute top of the rank,

this is the number one factor, there's no support for that.

Perhaps you might be able to say that soil structure is one of the factors influencing soil quality,

but the author doesn't have to assume that it's the number one factor.

The argument wouldn't be heard if it was the second most important or the third most important.

So that's why C is not necessary.

Now to be even more technical about this,

when you look at the conclusion, it's actually only about what's required to improve the soil structure.

But the author never then further connects improving the soil structure

to the soil quality of the farm field.

So you could also get rid of C on that basis as well.

The conclusion is really just about soil structure.

So now let's take a look at A, D, and E.

if not all, farmers in the region who abandon the use of chemical fertilizers

will periodically grow alfalfa.

Now there's a couple of reasons A is not necessary.

But before I get into that, I just want to make clear that this phrase,

if not all, is completely meaningless right now.

Do not get tripped up by an answer choice or any sentence at all, really,

that says most if not all or many if not all.

The if not all part adds absolutely nothing to the meaning of the sentence.

Because what it's just saying is, if not everyone, then most.

Okay, so what at a minimum is true then? Most.

So just read this as most farmers in the region who abandon the use of chemical fertilizers

will periodically grow alfalfa.

Now the first reason A is not necessary is the word most, which means over half.

Does the author have to believe that over 50% of farmers

who abandon chemical fertilizers will periodically grow alfalfa?

Why does it have to be over half? Why couldn't it be 49% of farmers?

That's still a very large proportion.

The argument is not weakened if this most actually were just 49% of farmers.

So that's one reason A is not necessary.

Now the next reason to give an answer choice A is that it is very specific about alfalfa.

A is saying that most farmers who abandon fertilizer will grow alfalfa.

This specific green manure crop alfalfa.

But notice in the stimulus that alfalfa is just an example of one of these green poop crops.

The author says such as alfalfa.

But there could be many other kinds of green manure crops.

So why would the author have to think that the farmers are going to grow this one specific kind of crop?

That's not what the author assumes.

The author does assume that in order to grow at least some kinds of green manure crop

we have to get farmers to abandon the use of chemical fertilizer.

But there is no reason the author needs to be so specific about that specific kind of crop.

Now the final reason that A is definitively wrong is a little bit more subtle.

But I still think it's worth pointing out.

You can actually get rid of answer choice A because the author's conclusion

is not actually asserting that if you get the farmers to abandon the use of chemical fertilizers

then that will improve soil structure.

What the author is saying is that this is necessary.

It is necessary you have to get them to stop using chemical fertilizer

if you want a chance of improving the soil structure.

But that doesn't mean that the author thinks getting farmers to stop using chemical fertilizers

actually will lead to growing green manure and actually will lead to improved soil structure.

This is just something that is necessary.

But the author is not saying that it is sufficient to cause green manure crops to be grown.

So that is a third reason to get rid of answer choice A.

And if you're confused by that, wait till I get to the right answer

because you'll see that the right answer does not make that confusion of sufficiency and necessity.

have a destructive effect on the soil structure of farm fields.

Well no, this is not necessary because the author's logic here

is that chemical fertilizers are stopping the farmers from growing green manure.

And because they're not growing green manure crops, that is what is leading to poor soil.

Remember, they used to grow green manure crops to rejuvenate the soil.

So what happened was, when they started using chemical fertilizer,

they stopped growing crops, and the stopping of the growing crops is what led to poor soil.

That does not require the chemical fertilizers to have some destructive impact on the soil directly.

The author does not have to think that chemical fertilizers are like poisoning the soil.

Now it's easy to assume that that's what's happening

because, you know, chemical fertilizer you assume is like bad, toxic for the soil.

But that's not actually part of the argument.

So that's why the author does not have to assume anything about the direct destructive effect on the soil structure.

The fertilizers themselves do not have to have that effect.

What is happening is that the fertilizers caused the farmers to stop doing this other thing.

This other thing was helpful for the soil, in the author's mind.

Now if you're still confused by that, let me negate answer choice D

and show you that it doesn't weaken the argument.

The negation is chemical fertilizers themselves do not have a destructive effect on the soil structure.

That doesn't hurt the argument because even if the fertilizers do not have a destructive effect on the soil structure,

they can still be causing people not to do something that's helpful for soil.

So that's why D is not correct.

many, if not all, and many just means a lot.

It doesn't necessarily mean most.

Most means over half. Many does not commit the author to saying over half.

So many farmers in the region will not grow green manure crops

unless they abandon the use of chemical fertilizers.

This is necessary because E is essentially describing this part of the author's logic.

Remember, I said earlier that the author assumed this conditional relationship

that if the farmers use chemical fertilizers, they will not grow green manure crops.

E is expressing that idea that a large number of farmers in the region,

in order to get them to grow green manure crops, they have to not use chemical fertilizers.

And that's just the contrapositive of this relationship right here.

That is why E is the correct answer.

Notice that answer choice E just says that

abandoning the use of chemical fertilizers is necessary in order to grow green manure crops.

It does not say that abandoning the use of chemical fertilizers will lead them to grow crops.

That's a significant difference between A and E.

A is saying abandoning the chemical fertilizers will lead them to do it.

But actually what the author was assuming is that

abandoning chemical fertilizers is necessary in order for the growing of green manure crops.

If you want to approach E through negation, let me go ahead and negate E.

The negation of E is, it is not true that many farmers in the region

will not grow green manure crops unless they abandon chemical fertilizers.

In other words, the negation means,

you can still get many farmers in the region to grow green manure crops

even if they don't abandon chemical fertilizers.

And that idea would undermine the argument because

if you could get a lot of people to grow green manure crops

even though they are still using chemical fertilizers,

then we have no reason to think that we have to abandon chemical fertilizers

to get the soil back to where it was.

Why couldn't we just go back to growing green manure crops

and then maybe those crops can have their positive effect on the soil?

So the author must assume that in order to get a lot of farmers

to start growing the green manure crops,

we have to get rid of the chemical fertilizer.