#13 - Must Be True

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=14154)

The correct answer choice is (A)

This question concerns secondary substances, but the concept reference is too broad to produce a
workable prephrase. The process of elimination is likely to be more useful: any answer choice that
cannot be proven by the passage will be incorrect. As always, passage organization is key: secondary
substances are introduced in the first paragraph, and the evolutionary pressures exerted on them are
described in the second. Either paragraph can serve as a useful reference point.

Answer choice (A): This is the correct answer choice, although many students find it difficult
to prove that the natural mutations in question are “recent.” Read closely! While not all mutations
are recent, some are: In the beginning of the second paragraph, the author observes that secondary
substances “first appeared, and new ones continue to appear, as the result of genetic mutations in
individual plants” (lines 19-21, italics mine). Clearly, if new substances continue to appear, we can
infer that some of them are the result of recent mutations in plants.

Answer choice (B): It is entirely possible that most (if not all) secondary substances give their
plants both their distinctive taste, and their distinctive smell. The passage provides no indication that
secondary substances typically contribute to one or the other, but not both.

Answer choice (C): Although some secondary substances are detoxified by insects or stored safely in
their bodies, we have no evidence that this process alters the plants’ chemical composition.

Answer choice (D): This is an attractive, but incorrect answer choice. In the first paragraph, the
author mentions that only a few of these substances occur in any one species of plant (lines 11-
12). That does not mean, however, that some species of plants necessarily produce only one such
substance: this is possible, of course, but cannot be proven with the information provided.

Answer choice (E): Secondary substances are never described are regulators of plants’ production of
primary substances. A quick look at the first paragraph should be sufficient to eliminate this answer
choice.

[VamosRafa19]

I picked D over A. My thought process was that the passage did not support 'recent', while only a few could mean one. I read the explanation above but I don't follow how we can infer from the passage that just because new ones appear over time we can infer they are recent. What if there's an arbitrary schedule of every 100 years that one appears, you'd still get new ones all the time but if we are in year 70 are we to assume that's recent? How is recent defined?

[KelseyWoods]

Hi VamosRafa19!

As you've pointed out, "recent" doesn't have a precise definition--and that's precisely what makes it an easier answer choice to prove! We can't necessarily prove that these mutations took place within a specific time frame (e.g., within the last 2 years). But "recent" is a relative term. "Recent" as it applies to mutations might be a much longer time span than "recent" applied to the last time I got my hair cut. It's the somewhat vague nature of the term "recent" that makes it easier to prove.

"One," on the other hand, is a very specific term. As you stated, "only a few" is a vague term and could include "one." But it doesn't have to mean "one." And that's the difference. We can't use a general term to prove a specific term. But we could do it the other way around and use a specific term to prove a more general term. So if I know for sure I have one of something, then I could prove that I have only a few of something. But if I know for sure that I have only a few of something, I cannot prove that I only have one of something because I could have two or three or maybe even four!

In a Must Be True question, we are looking for something that we are certain is true. It is often easier to be certain about less certain/specific statements. For the more specific statements, you have to have specific statements in the passage to prove them. If we don't have a specific statement in the passage to prove that some plants specifically produce only one such substance, then we cannot choose answer choice (D).

Hope this helps!

Best,
Kelsey