The ancient Nubians inhabited an area in which typhus occurred, yet surprisingly few of their skeletons show the usual evidence of this disease. The skeletons do show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil. This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread. Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

So I chose (D), because it most directly speaks to the evidence in the argument, "tetracycline in their food...'. However, I do not know whether this would be a valid GMAT question. (A) also provides a perfectly reasonable assumption on which the argument depends. If the tetracycline entered bodies after those bodies had been buried, then clearly it was not responsible for preventing typhus.

In GMAT-land, I can't remember seeing an assumption question in which two answer choices are assumptions upon which the argument depends, but one of them speaks more directly to the text/conclusion. If this is valid, and it is simply slipping my mind as to ever having seen such a question, surely this question is a 700+. I'd be interested to see if anyone has encountered a similar question. If so, then this is definitely a valid question, and a toughie .
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Will vote for D because

Question type : Assumption (Strengthen the conclusion)

conclusion : tetracycline in food explains the low incidence of typhus among ancient Nubians.

Premise 1: skeletons do show deposits of tetracyclinean antibiotic produced by a bacterium common in Nubian soil.

Premise 2: This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread.

A. The tetracycline deposits did not form after the bodies were buried.
--> one of the premise already state that "skeletons show the usual evidence of this disease", so option A cannot be true

B. The diseases other than typhus to which the ancient Nubians were exposed would not be affected by tetracycline.
--> Out of scope nothing talking about another diseases

C. Typhus is generally fatal.
--> Doesnot strengthe the conclusion.

D. Tetracycline is not rendered ineffective as an antibiotic by exposure to the process involved in making bread and beer.
--> Provide additional evidence that will strength the conclusion. If the Tetracycline which acts as antibiotic is not destroyed in the process of making bread or beer, then we can correctly conclude that
tetracycline in food probably explains the low incidence of typhus.
Correct

using ANT
Tetracycline is rendered ineffective as an antibiotic by exposure to the process involved in making bread and beer.
This clearly contradicts the conclusion, if Tetracycline doesnot act as antibiotic, then incidence of typhus would have been higher

E. Bread and beer were the only foods eaten by the ancient Nubians which could have contained tetracycline.
--> wrong because thay cannot be only source as they were made from grains and bacterium flourished on the dried grain.

such a tricky question
Now, I think D is the correct one. Both A and D look correct, but what makes D the correct one, is the part that says "Thus, tetracycline in their food probably explains..."

Use negate technique for choice A: The tetracycline deposits FORMED after the bodies were buried.

If the tetracycline formed after the bodies were buried, this kind of antibiotic still did not relate to the tetracycline that produced by bacteria in beer and bread.
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ChrisLele
The conclusion of this argument is "Tetracycline in their food probably explains the low incidence of typhus among ancient Nubians" as in the last sentence. This means that author expects food to be a reason for presence of Tetracycline. I understand that presence of tetracycline can be linked a defender kind of assumption, but we also know that tetracycline has always been there in Nubian soil, making me to go away from A, and the conclusion here should defend the low incidence of typhus( and not the presence of tetracycline on skeletons).
Let me know if this sounds logical or even if there is some flaw here.

The source of this question is a CR document from a gmatclub member. It says the question is from gmatclub or MGMAT. Just hoping for this to be true now
gmat-prep-critical-reasoning-collection-106783.html#p840353

IMO D

Because on negating A we get. The tetracycline deposits did form after the bodies were buried (Nothing told about scenario before bodies were buried). this implies two statements.
1) Tetracycline formed only after bodies were buried
2) Tetracycline formed both before and after bodies were buried

1 inverses the conclusion but 2nd does not inverse the conclusion.

Hence D

Facts: few of the skeletons of Nubians show the usual evidence of the disease typhus even though they inhabited an area in which typhus occurred,. But their skeletons show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil. This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread.

Missing Information:There is no alternate explanation to what is shown in bold or it is not falsified, such as Tetracycline being rendered ineffective as an antibiotic by exposure to the process involved in making bread and beer.

Conclusion:Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

Choice D is the best match for the missing information.

Choice A seems very close. To eliminate one of the two, we have to focus on the reason for the conclusion. It is shown in bold. It means that the author believes that tetracycline was their in their food and this would eliminate A because choice A is more a premise. So actually attacking author's argument is showing tetracycline in the food is not responsible for the low incidence of the disease.
So the assumption of D saying that the tetracycline in the food is effective, is required.
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There is one more point, which makes A weak as an assumption. If tetracycline deposited from the soil into the skeletons of these bodies, it still does not explain why only "few of their skeletons showed the usual evidence of typhus. After all, the ancient nubians inhabited in the area where typhus occurred, making them more susceptible to the disease. Most of them would have incurred the disease when they were alive. Typhus would invade their bodies when they were alive.

The ancient Nubians inhabited an area in which typhus occurred, yet surprisingly few of their skeletons show the usual evidence of this disease. The skeletons do show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil. This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread. Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

Which of the following is an assumption on which the argument relies?
Conclusion- tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

(A) The tetracycline deposits did not form after the bodies were buried.

(B) The diseases other than typhus to which the ancient Nubians were exposed would not be affected by tetracycline.- irrelevant, we are concerned whether tetracycline in food explains the low incidence of typhus

(C) Typhus is generally fatal.- irrelevant

(D) Tetracycline is not rendered ineffective as an antibiotic by exposure to the process involved in making bread and beer.

(E) Bread and beer were the only foods eaten by the ancient Nubians which could have contained tetracycline.- irrelevant, the argument claims tetracycline in food

I was down to options A and D and chose option A.

A on negation, The tetracycline deposits did form after the bodies were buried.
D on negation, Tetracycline is rendered ineffective as an antibiotic by exposure to the process involved in making bread and beer.
Both options seem like assumptions to me.

AjiteshArun , GMATNinja , MagooshExpert , GMATGuruNY , VeritasPrepBrian , MartyTargetTestPrep , DmitryFarber , VeritasKarishma , generis , nightblade354 other experts - please enlighten
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The ancient Nubians inhabited an area in which typhus occurred, yet surprisingly few of their skeletons show the usual evidence of this disease. The skeletons do show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil. This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread. Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

Which of the following is an assumption on which the argument relies?

(A) The tetracycline deposits did not form after the bodies were buried.

Skywalker18, Our conclusion is that tetracycline explains why there was a low incidence of typhus. Our premises give an indication as to why we discovered that tetracycline was in use by these people. (A) tries to attack a premise by saying that the buildup occurred after death, but does this destroy our argument? For one, another premise does say that tetracycline is in the soil, so that would actually strengthen our argument on that front. Second, not taking this into account, just because the buildup occurred after doesn't mean that the people didn't take it. It is equally as likely that they ate the grains even if the buildup wasn't on the bones. We would need another assumption about how tetracycline only builds up on bones if it is consumed. Our premise is being used to show a presence of an item, but just because the presence is questioned doesn't mean that it wasn't effective or in use.
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They could both be assumptions, but, of the two, only (D) is necessary for arriving at the conclusion. If (A) is not true, the argument still has some decent support for the conclusion that the ancient Nubians consumed tetracycline when they consumed food. If (D) is not true, then the conclusion is virtually unsupported.

It's a funny question though, I have to admit, because the part about the bone deposits is part of the support for the conclusion, and that support does not work without (A).
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nightblade354 GMATNinja MagooshExpert MartyTargetTestPrep IanStewart

Can we somehow confirm that this is an official GMATPrep question? Usually, Assumption questions (1) have a big gap or (2) can be challenged. In the first case, a correct answer choice (assumption) closes the gap. In the second case, an assumption "kills" the challenge so that the argument can stand.

IMO, option (A) looks like a good challenger to the conclusion, which says that antibiotic probably explains the low incidence of disease in skeletons. If we negate (A) we literally say that antibiotic (that is generated from bacteria that sits in the soil) killed / cured the disease after the bodies were buried.

I agree that (D) is a bit stronger challenger than (A), but both are good. This is why I doubt that this is an official question.

Question looks legitimate to me. See my explanation above and let me know if that clears anything up.
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Hi nightblade354 I indeed read your post yesterday (few times)

I guess the reason why (A) is incorrect is because it attacks the premise. And you discussed what consequences this attack has. Option (D), however, directly addresses the conclusion. Without (D), the argument falls apart big time. Things are clear now. Thanks!

For me both A and D are valid assumptions. When negated both of them weaken the conclusion.

Then why is D correct and A is wrong. For that I have used simple logic.

There is a line of thinking where the all premises point directly to the conclusion. The answer choice may be related or based on any of the premises and negating them shall give the correct answer.

However in this difficult question we see that there is one premise connected to another premises which then leads to the conclusion.

So P1 ----P2----- Conclusion.

A when negated attacks P1 which then invariably negates P2 which then weakens the conclusion.

D when negated directly attacks P2 which weakens the conclusion. This out of A and D , D is the apt solution.

AndrewN kindly help me on this one. A seems as good as D. Maybe I’m missing something

Posted from my mobile device

+1

Please share your comments A vs D AndrewN sir:)

Hello, Shikhar22 and mSKR. One of the reasons I prefer a "missing link" strategy for CR assumption questions, as opposed to the more popular negation technique, is that I get to leave everything alone and simply drop in a line wholesale to test whether I can go from premise to conclusion seamlessly. Try (A) and (D), respectively, in this manner:

PASSAGE (premise): This bacterium [common in Nubian soil and that produces an antibiotic called tetracycline] can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread.

ANSWER: A. The tetracycline deposits did not form after the bodies were buried.

PASSAGE (conclusion): Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

It seems a little strange to discuss the Nubian diet as a premise, then insert information about tetracycline and skeletal remains, for which we have to reach back further in the passage to qualify, and then return to the idea of food being a primary determinant in the low incidence of typhus among ancient Nubians. I would not write off the answer, but I cannot say that X (the premise) connects to Z (the conclusion) through it. I would yellow light the answer in my first pass, but I would be hoping for a better, more fitting bridge to connect the two lines from the passage. Try (D) out in the same way:

PASSAGE (premise): This bacterium [common in Nubian soil and that produces an antibiotic called tetracycline] can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread.

ANSWER: Tetracycline is not rendered ineffective as an antibiotic by exposure to the process involved in making bread and beer.

PASSAGE (conclusion): Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.

Wow, if that is not a perfect bridge or "missing link," then I am not sure what more we could want. The premise mentions the diet of the ancient Nubians, the answer choice rules out the possibility that an active antibiotic compound suspected to be a part of that diet would be rendered ineffective prior to consumption, and then the conclusion about food follows. This is a green light answer, one that we cannot find fault with.

Between (A) and (D), then, the latter is directly related to the premise and the conclusion that follows, so it is the safer bet, and we should choose it. The order in which the sentences are presented in the passage is crucial to the process I have outlined. Anyway, I hope that helps. Just remember that when you find friction, you are probably not pursuing the path of least resistance, and in Verbal, that often translates into a wrong answer.

Good luck with your studies.

- Andrew

Thank you so much for such a detailed explanation. Amongst all the chaos, I never quite got hold of this technique for assumption questions. Negating answer choices always gave inconsistent answers. This seems a more logical and efficient way of dealing with assumption questions. I’ll be working with this technique from now on! Thank you again for the explanation!