#2 - The teeth of some mammals show "growth rings" that

[Administrator]

Complete Question Explanation

Must Be True. The correct answer choice is (C)

The pigs develop two new rings on their teeth every year: opaque rings in the summer and translucent ones in the winter. On the teeth found, the last ring was translucent, and was only about half as wide as was normal.

Because the last ring was only half formed, we know that the pigs probably died halfway through a season. And, because the ring being formed was translucent, it seems that this happened in winter.

Answer choice (A) cannot be right, because it would imply that the last opaque ring was smaller than normal, but we do not see that at all.

Answer choice (B) assumes that the teeth had the same number of rings, but we have no evidence of that.

Answer choice (C): This is the correct answer choice. Putting together the inferences from the stimulus, it seems that this animal died halfway through winter.

Answer choices (D) and (E) are probably wrong because the teeth were found in a trash pit – they were probably killed for food, not from a catastrophe or starvation.

[lexigibbs]

I have a question about the homework question from Logical Reasoning. I am confused how the answer is correct.

L1 HW Must Be True 1-88/11 the correct answer is C I thought it would be D or E

I hope you can clarify how the right answer to this came about!

Thanks!!

[Jonathan Evans]

Hi, Lexi!

First off, you should review the lesson to make sure that you are solid about what you're looking for in a credited response to a Must Be True question or a Main Point question and that you know the common traps and characteristics that make other answer choices incorrect. This takes a lot of practice, and you've got to have a firm grounding in the fundamentals.

Now for your question.
Question 11: Must Be True

Stick to the facts! What do we know? We get opaque bands on the teeth in the summer. We get translucent bands in the winter. Since on the last bands we always find narrower than usual translucent bands, we know that the last band, a translucent band, did not get a chance to finish depositing. Therefore, the animals' lives were interrupted during the translucent deposit time, which according to the facts happens in the winter.

(D) and (E) introduce outside suppositions. You have to stick to what you can prove.

I hope this explanations helps. Please follow up should you need further detail!

[speedymc36]

Answer choices (D) and (E) are probably wrong because the teeth were found in a trash pit – they were probably killed for food, not from a catastrophe or starvation.

Would you also be able to rule out answer choices D and E because it is out of scope? You would not be able to know for sure from the stimulus.

[Emily Haney-Caron]

Hi speedymc,

Because this is a Must Be True question, D and E are wrong because either could be true, or an entirely different thing could be true; so, even though D and E could maybe be true, they are not necessarily true. I think that's what you were saying; if so, great job thinking this through!

[uhinberg]

This was clearly the only possible answer that was right, but again, this doesn't appear to have to be true. The stimulus only says that the cementum is deposited "constantly"; it says nothing about the rate at which it is being deposited. Perhaps it is deposited at a far greater rate at the beginning of the season. So, answer C is most strongly supported by the stimulus, but it seems wrong to classify it as "must be true."

[Ricky_Hutchens]

Hi uhinberg,

C must be true in this case because the stimulus says not only that the cementum is deposited constantly, but also that it is opaque in the summer and translucent in the winter. Because the last ring is translucent, that means that the animals must have died in the winter. If they had made it to the summer, then the constant deposit of cementum would have created an opaque ring around the translucent ring.

Hope that helps.

[nlittle]

Hello,

I had an issue with the modifier in this one. The first sentence states that "some" mammals show growth rings that result from the depositing of cementum as opaque during the summer and translucent during the winter.. Because the author states that this applies to "some" mammals, I am having trouble understanding why there may be any reason to believe this applies to these pigs without the author stating so.

While the author states that the pigs do have bands, he or she never states that these bands were the same bands referenced in the first statement, and even if they were the same bands, the first statement does not state that these rings exclusively result from cementum and its relationship with seasonality. For example, a cow could have the bands as a result from the authors statement while pigs could have the same bands resulting from its diet.

Could you please help me understand how, in this case, "some" applies to the pigs without drawing a direct connection? It becomes difficult to distinguish when an author wants us to take information as literally as possible (such as how I am approaching this) and when an author expects us to accept an implication not stated in the stimulus.

Thanks,

Nick

[Luke Haqq]

Hi Nick,

I can understand that the answer might feel a bit frustrating, given the "some" language, and the fact that this would be classified as a must-be-true/inference question. In the end, my best suggestion is that this question's subject matter and context is about a paleontologist (presumably) who is trying to infer something about remains that the paleontologist has found. As such, it appears that the author is reasoning via induction rather than deduction, but we are supposed to take that as a given.

Suppose, during the excavation of the Stone Age trash pit, it were true that "All mammals show growth rings that result from the constant depositing of layers of cementum as opaque bands in summer and translucent bands in winter," then the paleontologist would indeed be able to infer (deduction) that the rings found in pig's teeth were these types of rings mentioned in the first sentence. Instead, this stimulus involves the inference (induction) that moves from the observation of given excavated teeth, to the conclusion that the observation fits under the theory in the first sentence. As I understand, the fact that it appears to rely on induction might be why it seems frustrating as a must be true question. However, given that we are supposed to take the statements in the stimulus as true, it's true that the author of the stimulus is reasoning via induction rather than deduction, but we can still ascertain what must be true within the author's argument structure. If the author has (implicitly) inferred via induction that the translucent teeth rings found on a given mammal remains (pigs) were the rings mentioned in a theory about translucent teeth rings on "some mammals," then the "most strongly supported" conclusion is that the pigs that were excavated died "roughly in midwinter" (because the theory in the author's argument says translucent bands develop in the winter, and the author induces that this is the case with the translucent teeth rings in discovered mammal remains).

[rjulien91]

I don't understand why the answer to this is C versus A.