Source: Official Guide Revised GRE 2nd Ed. Part 9; Section 4; #25


Which of the following, if true, most

Which of the following, if true, most seriously weakens the argument? The average temperature of the lobster-rich waters off the coast of Foerkland has been increasing for some years. In warmer water, lobsters grow faster. In particular, lobster larvae take less time to reach the size at which they are no longer vulnerable to predation by young cod, the chief threat to their survival. Consequently, the survival rate of lobster larvae must be going up, and the lobster population in Foerkland’s coastal waters is bound to increase. There are indications that in recent years the fishing fleet operating off the coast of Foerkland has been taking cod at an unsustainably high rate., The increase in water temperatures off Foerkland has not been as pronounced as the increase in average soil temperatures in Foerkland., Because of their speeded-up growth, lobsters now get large enough to be legal catch before they reach reproductive maturity., Even though lobsters grow faster in warmer waters, warmer waters have no effect on the maximum size to which a lobster can eventually grow., Cod are a cold-water species, and the increasing water temperatures have caused a northward shift in Foerkland’s cod population.

5 Explanations


Tanima Shukla

Hi! I answered with choice E, but I somewhat understand why C would be a better option.

The fact that the cod population is moving northward strengthens the argument because there are less predators to feed on the larvae, which in turn allows the larvae to reach maturity with little risk. Now that I’m analyzing it, it’s a similar logic to choice A.

Is my logic on the right track?

Aug 10, 2018 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Tanima :)

Ok, so in this problem, the main conclusion is that the adult lobster population will increase as water temperatures increase. The reasoning is that as lobster larvae are maturing faster, they are less vulnerable to cod and thus their survival rate is increasing. There are definitely a lot of assumptions to this argument, and we're looking for the statement that best exposes one of these assumptions.

(A) doesn't directly address the size of the adult lobster population nor does it talk about the population of young cod. So, it doesn't do a really good job of strengthening the argument, while it does nothing to weaken the argument.

(E) also could strengthen the argument but again is not directly related to the size of the adult lobster population.

(C) weakens the argument because it provides a reason why the adult lobster population may not actually increase despite an increases larvae survival rate.

Again, (C) speaks directly to the argument (that the adult lobster population will increase) and provides evidence against this assumption. That's why it is the best answer to weaken the argument :)

I hope this helps!

Aug 10, 2018 • Reply


Anna Roberts

I am just confused as to why A is not weakening?
When there is another reason instead of the conclusion given isn't that a weakener?

I am trying to compare this to ETS practice exam#1 Q7 -- where another reason would have been a weakener.

Can someone please help?

Jonathan , Magoosh Tutor
Hi Barun,
What you are saying makes sense! :) But that's not the question we are trying to answer; it's not relevant to the argument.
The conclusion is about the reason insurers in Sparva pay more--the argument is that the less restrictive policy leads to paying more.
The fact that there are NOT more accidents in Sparva supports this conclusion.
***If there were MORE accidents, then this would weaken the the conclusion, because more accidents would be an alternate explanation for higher payments.***

Nov 22, 2017 • Comment


Hi Radhika,

(A) does not weaken the argument because if (A) were true, then the argument would be strengthened.

The argument is that the lobster survival rate is increasing because lobsters are less vulnerable to cod because they're reaching maturity at a faster rate than before.

(A) indicates that there are fewer cod. Now, this COULD weaken the link between (1) increasing lobster survival rate and (2) faster maturity, but it doesn't weaken the argument that " the survival rate of lobster larvae must be going up, and the lobster population in Foerklands coastal waters is bound to increase." This part of the argument is strengthened if cod are being taken, because cod eat lobsters.

The question asks which choice most seriously weakens the argument, and (C) definitely weakens the argument more than (A) does, so (A) must be incorrect.

Nov 22, 2017 • Reply


Malak Kudaimi

I can definitely see how C works, and in fact I was going back and forth between it and D. Why isn't D also a possibility?

Nov 5, 2017 • Comment


Hi Malak,

(D) states: Even though lobsters grow faster in warmer waters, warmer waters have no effect on the maximum size to which a lobster can eventually grow

So this indicates that lobsters will grow faster, but not bigger. The argument is only concerned with the number of lobsters, not their size. Since (D) only tells us about their size, this choice is not relevant.

Does that make sense?

Nov 14, 2017 • Reply


Gravatar Sam Kinsman, Magoosh Tutor

Hi Aanand,

Keep in mind that option C tells us that the lobsters are legal to catch before they can reproduce. If many lobsters are caught before they reproduce, this will make the population decline. You're right that we don't know for sure that the lobsters are actually being caught, but if they are, this answer choice clearly weakens the argument!

Also, notice that answer A simply gives us an additional reason why the lobster population would increase. If A is true, then the population is probably increasing for two reasons: (1) there are fewer cod, and (2) more lobster larvae are surviving because of the increase in temperature. So the argument is still valid.

Nov 20, 2015 • Comment


Gravatar Chris Lele, Magoosh Tutor

Dec 8, 2012 • Comment

Aanand Nayyar

Chris, increasing the temperature makes lobsters grow faster (but this doesn't necessarily imply there are more lobsters). The argument is that "because lobsters are no longer vulnerable, the population increases" (the last sentence uses the word "Consequently").

Option C doesn't directly talk about a decrease population, it just says that it's legal to catch the lobsters because they are large enough early on. This has two aspects:

1. You can catch them early but they are growing fast as well, so population needn't increase.

2. Just because they are legal to catch, doesn't mean they are actually caught!

I feel that Option A is correct, as it undermines the word "Consequently" in the argument.

I hope I make sense.
Hoping for a reply!

Nov 16, 2015 • Reply

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