#17 - Must Be True

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=7945)

The correct answer choice is (A)

Passage Exclusivity questions ask about information contained in only one of the two passages.
Since this question refers to fiber and grit in a diet, recall that their role was discussed in the second
paragraph of Passage B. A thorough understanding of passage organization allows for quick access
to the information necessary to attack questions involving a concept reference.

Answer choice (A): This is the correct answer choice. While too little fiber and grit diminish
tooth wear and increase caries frequency, too much fiber and grit can expose a tooth’s pulp cavity
and can also result in caries (lines 47-50). Therefore, fiber and grit can either limit or promote caries
formation, depending on their prevalence in the diet.

Considering the unusual effect of fiber and grit on caries formation, it would have been wise to
highlight or underline lines 47-50 in Passage B, especially since the topic of fiber and grit is unique
to that passage.

Answer choice (B): This is a Shell Game answer. Although increased reliance on agriculture
increases the consumption of carbohydrate-rich foods, there is no evidence that it also increases the
consumption of fiber and grit. As far as we know, there were no changes in the tooth wear between
Early and Late Ban Chiang Groups (lines 61-63).

Answer choice (C): Since the nutritional value of fiber and grit was never addressed in either
passage, this answer choice is incorrect.

Answer choice (D): This is an Opposite answer. Recall that tooth wear removes fissures on tooth
surfaces, whereas the reduction of fiber and grit diminishes tooth wear (lines 45-48). Clearly, as
long as tooth wear is not severe, fiber and grit would not contribute to the formation of fissures in
tooth surfaces; on the contrary—they may help wear down the tooth surfaces enough to remove the
fissures in them.

Answer choice (E): The effect of fiber and grit on the stickiness of carbohydrate-rich foods was
never addressed in either passage. This answer choice is incorrect.

[lp1997]

Hi,

I don't see how choice A is supported in paragraph 2. The paragraph only says that both a large amount and a small amount of fiber can increase carie formation. The paragraph does not mention how fiber and grit may decrease caries formation.

B seemed to be a very good answer here. The passage said that alterations in tooth wear that accompany a shift to an agricultural society. It then set forth how fiber and grit can reduce tooth wear and increase caries.

Where did I go wrong here? Thank you!

[Daniel Stern]

Hi LP:

The Administrator's post above addresses the problems with answer B quite well:

Answer choice (B): This is a Shell Game answer. Although increased reliance on agriculture
increases the consumption of carbohydrate-rich foods, there is no evidence that it also increases the
consumption of fiber and grit. As far as we know, there were no changes in the tooth wear between
Early and Late Ban Chiang Groups (lines 61-63).

As for answer choice A, that second paragraph states that "a reduction of fiber or grit may diminish tooth wear," increasing caries. This sentence implies that the fiber or grit causes tooth wear. The next sentence goes on to say that too much wear can also cause caries. If too little wear can cause caries, and too much wear can cause caries, and the fiber/grit causes the wear, we can combine these two concepts to reason that too little fiber can cause caries, and too much fiber can cause caries.

Answer A sums this up nicely for us: the effect of the fiber and grit depends on how much of it we have in the diet.

I hope this helps. Good luck!
Dan

[fersian]

Hi. I'm having trouble seeing the support for the section of 'A' that states that fiber and grit can limit caries formation.
Is it line 45-46? If so, how do we know that 'the wearing down of tooth crown surfaces' is interchangeable with increased consumption of starchy-sticky foods?
And is starchy-sticky foods synonymous with fiber and grit?

I'm not sure if this is a trick on LSAC's part for using synonymous words...

[KelseyWoods]

Hi Fersian!

"Starchy-sticky foodstuffs" is not synonymous with "fiber and grit." Lines 42-44 tell us that the frequency of caries can be increased by 2 factors: 1) "increased consumption of starchy-sticky foodstuffs" and 2) "alterations in tooth wear." The next few sentences expand on how alterations in tooth wear can increase caries frequency. Lines 45-46 tell us that tooth wear can reduce caries by removing fissures. Lines 47-48 tell us that reducing "fiber or grit" may diminish tooth wear, thus increasing caries (since we know from the previous sentence that tooth wear can reduce caries). So the passage tells us that if you reduce fiber or grit, you reduce tooth wear, thus suggesting that fiber or grit result in tooth wear, which can reduce (or limit) caries by removing fissures, or expose a tooth's pulp resulting in caries (lines 49-50).

Hope this helps!

Best,
Kelsey

[Albertlyu]

hi Kelsey,

thank you for your explanation, please may I ask if you could elaborate on this part?

:" the wearing down of tooth surface reduces caries formation by removing fissures that can trap food particles. A reduction of fiber or grit in a diet may diminish tooth wear."

So the fiber or grit reduces tooth wear, and what the wear does is removing fissures, therefore fiber or grit increases fissures as described in answer choice D. please may I ask what went wrong with my reasoning? thanks.

Albert

[Adam Tyson]

A reduction of fiber or grit in a diet may diminish tooth wear.

That's a potentially confusing sentence, Albert, almost like a double negative (reducing something that reduces something else), and it appears that you interpreted it to mean the opposite of what it actually means. To paraphrase that sentence, it is saying that if you have less fiber or grit, you won't wear your teeth down as much.

Tooth wear doesn't create fissures, but removes them. Apparently, it is fiber or grit that contributes to wearing you teeth down, making them smooth and removing fissures that can lead to dental caries. Think of it like sandpaper taking out the cracks and dents in a piece of wood. That should help you get your head around this one and see why answer D is an opposite answer.

[Albertlyu]

A reduction of fiber or grit in a diet may diminish tooth wear.

That's a potentially confusing sentence, Albert, almost like a double negative (reducing something that reduces something else), and it appears that you interpreted it to mean the opposite of what it actually means. To paraphrase that sentence, it is saying that if you have less fiber or grit, you won't wear your teeth down as much.

Tooth wear doesn't create fissures, but removes them. Apparently, it is fiber or grit that contributes to wearing you teeth down, making them smooth and removing fissures that can lead to dental caries. Think of it like sandpaper taking out the cracks and dents in a piece of wood. That should help you get your head around this one and see why answer D is an opposite answer.

thank you Adam for your reply! Really appreciate your time and attention.

Albert