#11 - A mass of ''black water" containing noxious organic

[Administrator]

Complete Question Explanation

Assumption. The correct answer choice is (D)

The argument concludes that the black water event that struck Laurel Bay last year was more intense than it has been in at least two centuries. The author supports this conclusion by noting that five species of coral, which were more than two centuries old, were wiped out during that particular event. In other words, since the coral had survived for over two hundred years until last year’s black water event, there could not have been another black water event of the same intensity during that period of time.

The author fails to consider other possible explanations that may have contributed to the elimination of these five coral species from Laurel Bay. The argument assumes that all other potential factors relevant to the elimination of a coral species did not contribute to their elimination. Any answer choice that addresses one of these potential factors and eliminates it from consideration would represent a Defender Assumption.

Answer Choice (A): The author does not need to assume anything about the frequency of black water events. The five coral species have survived for over two hundred years, and that indicates that last year’s event is the most intense in two centuries. This does not depend on how frequently other events have struck the bay over the past two centuries.

Answer Choice (B): While this answer choice strengthens the argument, it is too strongly worded to be an assumption. The argument does not require that every species of coral be seriously harmed. The argument focused only on the five species that were wiped out, not all coral species in the bay.

Answer Choice (C): The Assumption Negation technique destroys this answer choice. If the mass of black water did decimate other plant or animal species that make use of the coral, this would actually strengthen the argument, as it would further support the conclusion that last year’s event was an especially intense event. The correct answer choice should weaken the argument once the Assumption Negation technique is applied, not strengthen it.

Answer Choice (D): This is the correct answer choice. This answer choice is a classic Defender Assumption. The Assumption Negation technique is particularly effective in identifying this assumption. If the mounds of coral were in especially fragile condition just before the black water swept into Laurel Bay, then their condition might have made them especially vulnerable to a black water event. Last year’s black water event would not have needed to be the most intense black water event of the past two centuries in order to wipe the coral out. Since the logical negation of this answer choice weakens the argument, this answer choice is correct.

Answer Choice (E): This answer choice weakens the argument. If older specimens of coral are more vulnerable to damage than young coral, then the five species that were wiped out may have been more vulnerable to damage. The coral could have survived more intense black water events in the past when they were younger and less vulnerable. This weakens the argument as it suggests that there may have been black water events of the last two hundred years that were more intense than the recent event.

[rachel9876]

Hi, I was having trouble deciding between answer choices D and E.

When I initially read answer choice E I interpreted "older specimen" to mean that they have been alive for longer and thus are older, as opposed to your interpretation of older meaning specimens from a longer time ago. From my interpretation, answer choices D and E seemed to be very similar.

How did you know which way to interpret it/are there any other ways to eliminate answer choice E?

Thank you in advance!

[Frank Peter]

Hi Rachel,

Whenever we encounter an argument in the LR section, it's always helpful to start by thinking about potential problems with the argument's line of reasoning.

Here, the conclusion is that "even if this black water phenomenon has struck the bay before, it did not reach last year’s intensity at any time in the past two centuries." The "intensity" is supposedly indicated by the wiping out of five species of coral, including mounds that were more than two centuries old. But what if wiping out these mounds of old coral isn't actually a reliable indicator of the intensity? That's the potential weakness with our argument that the correct answer choice has to fix - it's a Defender assumption.

(E) weakens the argument (and is therefore not the correct answer) because if older specimens of coral were more vulnerable to damage, that means their destruction may not be all that reliable an indicator that this was an especially intense mass of black water. It could have been no more intense than it was in the past - just in this case, the coral was more vulnerable.

(D) strengthens the notion that this was an especially intense incidence of black water since the old coral that was destroyed was in otherwise good condition before the black water swept through.