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I’m confused as to why d is right for #15 because it says “major changes” and the passage discusses “when deviations from normal are quite small” (line 23) and how it fluctuates between 1 to 2 %. Because of this discrepancy I eliminated d .
 Adam Tyson
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Thanks for the question, fg6118. This is a pretty dense science passage, and prephrasing the main point might be a bit of a challenge, but it seems to be something about hormones affecting behavior in order to maintain balance within the body (something about water levels and salt). It seems that these hormones come into play when the body goes out of whack by more than the normal range of 1-2%. It's that normal range that you found reference to at line 23.

Take a look a little farther along, around line 31, and you'll find this language:
Nevertheless, the concentration of solutes in extracellular fluid may at times become elevated or reduced by more than the allowed tolerances of one or two percent. It is then that complementary physiological and behavioral responses come into play to restore plasma osmolality to normal.
Those deviations beyond the normal range are the "major changes" referred to in answer D, and that is what the passage is ultimately about. The rest of the passage talks about how the body responds by either retaining or releasing vasopressin, a peptid hormone, which either inhibits or causes thirst, among other reactions, to bring the body back to homeostasis.

Definitely a challenging passage! Remember to start by prephrasing the main point to the best of your ability, so that you can more easily sort losers and contenders. The other answer choices should fall away, leaving D as your only contender.

Keep up the good work!
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Answer choice D is fine, when considered on its own. But then answer choice E reads, "The mechanisms regulating reproduction are similar to those that regulate thirst and sodium appetite"

Answer choice E includes an important aspect of the article's framing: the discussion of the traditional conception of the role of hormones in influencing the body's biological/reproductive functions. Answer choice D completely elides this discussion, while E includes that discussion, and, implicitly, the discussion referred to in answer choice D, which is a specific example of the way hormones can impact behavior in a way that was previously considered to be reserved for only biological/reproductive functions.

When considering the "main point," often the more general answer is more apt, because it offers a more complete picture of the article's discussion. So how can it be expected that one should select either one of these valid and true statements (answer D or E) over the other?
 Zach Foreman
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Good question, pf

Answer choice E is incorrect because it seems to give equal weight to reproduction as osmoregulation. However, reproductive hormones are only mentioned in the first sentence and then never again. In contrast, lines 9-58 discuss regulation of how the body balances solutes in body fluids.
This is a good example of how not paraphrasing could lead you astray. I don't think you would put reproduction in a ten word prephrase.
E is deficient in that it doesn't use the word hormone (choosing the vaguer "mechanism") which should be a part of any main point answer. The real compare/contrast in this passage is not between reproduction and fluid balance but between hormones biological effects and its behavioral effects, which again, is absent in E but present in the correct answer, D.
In testing this, you could try to work backwards. If you were to write an essay using E as the main point, I think you would include much more discussion about reproduction. You would probably include parallels between reproductive mechanisms and thirst/sodium mechanisms.
Thesis statement: Reproduction and fluid balance are governed by the body using similar mechanisms.
Body paragraph I: First example of how thirst and reproduction are similarly governed
Body II: Example 2 of how they are similarly governed
Conclusion: they are similar
But if you were to back-plug D, you would get something like this:
Thesis statement: Hormones regulate the body using both physiological and behavioral responses.
Body I: Physiological changes to hormone response to changes in osmality
Body II: Behavioral changes to hormone response to changes in osmality
Conclusion: these two changes complement one another
We can see that the second example is basically what is going on in the paragraph, with a heavy dose of explanatory text in the first paragraph. The argument really gets going at line 34 (and was summarized in lines 6-9). The appearance of both behavioral and physiological effects of hormone regulation is the key to this passage. It is wholly absent in E.

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