LSAT and Law School Admissions Forum

Get expert LSAT preparation and law school admissions advice from PowerScore Test Preparation.

 Administrator
PowerScore Staff
  • PowerScore Staff
  • Posts: 8919
  • Joined: Feb 02, 2011
|
#40960
Complete Question Explanation

Must Be True, SN. The correct answer choice is (B)

The stimulus contains a fact set and features conditional reasoning, which is identifiable by the use of the necessary condition indicator “unless” in the first sentence. Applying the Unless Equation, the phrase modified by “unless” becomes the necessary condition, whereas the remainder is negated and becomes the sufficient condition. However, you should notice the sufficient condition indicator “any” modifying the clause “antibiotics used against the bacteria,” which needs to be factored into the relationship.

Thus, if the bacterial species does not become resistant to the antibiotics used against it, then either the antibiotics did not completely eliminate the bacterial species, or no antibiotics were used against it:
PT62 - LR2 #11 diagram 1.png
In the contrapositive form, if any antibiotic is used against the bacterial species and that antibiotic does not completely eliminate it, the bacterial species will develop greater resistance to that antibiotic. Some students would prefer to diagram the contrapositive first, since the “unless” modifier is logically equivalent to the phrase “if not.”

The second premise tells us that no single antibiotic now on the market is powerful enough to eliminate bacterial species x:
PT62 - LR2 #11 diagram 2.png
Therefore, we can use the contrapositive of the conditional relationship in the first premise to prephrase the conclusion that if any antibiotic is used against bacterial species x, the species will become more resistant to it (since the other sufficient condition has already been established):
PT62 - LR2 #11 diagram 3.png
This prephrase is tremendously helpful in attacking the answer choices and immediately proves that answer choice (B) is correct. Because stimuli containing conditional reasoning in combination with Must Be True questions frequently produce contrapositive answer choices, you should apply the contrapositive and prephrase an answer choice based on the contrapositive.

Answer choice (A): On the basis of the evidence presented in the stimulus, we cannot estimate the likelihood that an antibiotic can be developed to eliminate bacterial species x. Although no single antibiotic now on the market is powerful enough to eliminate bacterial species x completely, it is impossible to predict what can happen in the future.

Answer choice (B): This is the correct answer choice, which predictably contains the contrapositive of the first sentence of the stimulus: because no single antibiotic now on the market is powerful enough to eliminate bacterial species x, any antibiotic used against the bacterial species will become more resistant to it.
PT62 - LR2 #11 diagram 4.png
Answer choice (C): At first glance, this may seem like an attractive answer. If no single antibiotic now on the market is powerful enough to eliminate bacterial species x completely, is it not likely that the only way of completely eliminating bacterial species x is by combining two or more antibiotics? Unfortunately, we are looking for an answer that Must Be True, not just likely to be true. There is always the possibility that there are other ways to completely eliminate bacterial species x (take across-the-board mandatory immunizations, for instance). Because we have no information as to whether there are other ways to eliminate the bacterial species in question, this answer choice cannot be proven by the stimulus and is therefore incorrect.

Answer choice (D): Although no single antibiotic is powerful enough to eliminate the bacterial species x, perhaps there are other ways to eliminate it (vaccinations, a combination of several different antibiotics, etc.). Even if those ways did not work, it would still be unreasonable to conclude that the bacterial species in question will inevitably become more virulent. The topic of virulence was never discussed in the stimulus, and therefore cannot be proven by the information in it.

Answer choice (E): This appears to be an attractive answer because we do know that a bacterial species will inevitably develop greater resistance within a few years to any antibiotics used against it, unless those antibiotics can completely eliminate it. Clearly, no antibiotic on the market can completely eliminate bacterial species x. However, we cannot be 100% certain that the bacteria today is more resistant to some of the antibiotics that have been used against it in the past, because we do not know when (or whether) these antibiotics were actually used. The author clearly states that it takes a few years for the bacterial species to develop greater resistance to any antibiotic that fails to completely eliminate it. Therefore, if the ineffective antibiotics were used only a few months ago, we cannot expect that the bacteria are more resistant to them today than it was before they were used.
 netherlands
  • Posts: 136
  • Joined: Apr 17, 2013
|
#9919
Hi there PS,

I chose A on this one, but only after thiking on E for a couple of seconds. I eliminated E basically because technically Species X would be resistant to Any/All antibiotics that had been used against it based off of the stimulus ( not At least some... even though I guess "some" can encompass "all") - but also because there's a chance that it hasn't yet formed a resistance to any of them because it takes a few years and we wouldn't know how much time had passed since any antibiotic had been exposed to X making B stronger?

I do see how B is the more straightforward answer - but I just want to also understand why I'm eliminating E, since it too could be true ... but is not a must be true.
 Steve Stein
PowerScore Staff
  • PowerScore Staff
  • Posts: 1153
  • Joined: Apr 11, 2011
|
#9922
Hey Netherlands,

Sounds like you've got it; at this point, there is no way to know how long bacterial species X has been around, or whether it has already increased its resistance to any particular antibiotic.

I hope that's helpful--let me know whether this answers your question--thanks!

~Steve
 rneuman123@gmail.com
  • Posts: 38
  • Joined: Aug 17, 2016
|
#27916
I chose c on this one. It makes the most sense to me because the stimulus says "no single antibiotic" could eliminate the bacteria. Can you explain why B is more strongly supported than C?
 Adam Tyson
PowerScore Staff
  • PowerScore Staff
  • Posts: 5153
  • Joined: Apr 14, 2011
|
#27936
(In a Seinfeldian voice): Neuman! (Sorry, I had to.)

The problem with answer C here is the very strong claim of "only". How do we know, based on the stimulus, that the only way to eliminate X is through a combination of antibiotics? Maybe I could instead develop a vaccine, or use some fancy old-school phage therapy (that's a thing - we even have a reading comp passage on it somewhere) or attack it with phytochemicals instead of antibiotics (also a thing - same RC passage)? Maybe I could drop a nuke on it? Perhaps I could take all the organisms that carry X and isolate them somewhere, and then wait for all those organisms and their offspring to die off, thereby driving X to extinction due to a lack of hosts? You get my point. ;-)

Now, if C said "the only way that antibiotics could completely eliminate X would be to use two or more in combination", then we would be on to something, and that might be a really good answer. But C, as it is now, just goes too far to be proven by the limited scope of the stimulus.

Ooooh, I got another one! Make X watch C-Span for days on end until it dies of boredom!

The lesson to take away from this one is to beware of "only", "best", and other strong words or ideas like those. On MBT questions, they are typically too strong to prove. Try to think of an alternative, even a silly one (Hypnotize all the X and make them jump into a vat of acid!), and if you can come up with one that works and doesn't contradict the evidence given in the stimulus, then that strong answer is not the right one.
 rneuman123@gmail.com
  • Posts: 38
  • Joined: Aug 17, 2016
|
#27946
lol. Thanks! With those awesome examples, I don't think I'll ever forget the strength of words like 'only' again!
 bk1111
  • Posts: 103
  • Joined: Apr 22, 2017
|
#34499
Hi, I read the explanation of why E should be eliminated, but I am not 100% about the reasoning behind it still. Can someone elaborate? Thank you!
 Francis O'Rourke
PowerScore Staff
  • PowerScore Staff
  • Posts: 471
  • Joined: Mar 10, 2017
|
#34583
Hi bk,

The key to understanding Choice (E) is that the Stimulus told us that bacteria will inevitably gain resistance unless it is eliminated by the antibiotic.

Choice (E) does not account for how much time has passed since Bacteria X has been exposed to the antibiotics, so we cannot be sure whether it has yet gained some resistance.
 Ispeakcritique
  • Posts: 3
  • Joined: Aug 31, 2018
|
#56782
Hi All,

I’m puzzled with this. If the line “Antibiotics used against it” is modified by the sufficient indicator “Any”, why does it become a necessary condition?

If a term is modified by “unless” then it becomes the necessary condition. And in this case it should only be “antibiotics eliminate that species completely”.

What am I missing here?

Thank you
 James Finch
PowerScore Staff
  • PowerScore Staff
  • Posts: 943
  • Joined: Sep 06, 2017
|
#56792
Hi I speak critique,

I believe you're referring to the conditional statement given in the first sentence of the stimulus. In that case, the correct way of diagramming it would be to make the term after the unless the necessary condition, then negate the other term and make it the sufficient condition, creating:

Greater ResistanceB(GRB) :arrow: Species Eliminate CompletelyB (SECB)

and its contrapositive:

SECB :arrow: GRB

Then we're told that species X is unable to be eliminated by any of the antibiotics currently on the market, effectively giving us the sufficient condition for the contrapositive. As a Most Strongly Supported question, this means that we should be looking to the contrapositive's necessary condition as the correct answer choice (here that species X will likely become more resistant to the antibiotics currently on the market.) Answer choice (B) fits the bill, and is the correct answer choice here. This is a very common setup for conditional Must Be True/Most Strongly Supported questions, testing the ability to understand contrapostives.

Hope this helps!

Get the most out of your LSAT Prep Plus subscription.

Analyze and track your performance with our Testing and Analytics Package.