Excavation in City Y found ten ships that all sank at the same time in the city's harbor, in one...

GMAT Critical Reasoning : (CR) Questions

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Excavation in City Y found ten ships that all sank at the same time in the city's harbor, in one sudden event in approximately A.D. 800. One possible explanation for the sinking is a tsunami, caused by a strong earthquake from a fault under the sea about fifteen miles away. However, it is more likely that a powerful storm sank the ships, since, if an earthquake had been responsible, there would also have been major damage to the city's walls and buildings—but there apparently was no such major damage, otherwise we would have discovered records from that time mentioning major building repairs.

Which of the following is an assumption on which the argument depends?

There is evidence that the fault in question had produced tsunamis earlier in City Y's history.

Some record-keeping practices existed in City Y around A.D. 800.

City Y's harbor offered relatively good protection for ships from the effects of a storm.

City Y was wealthy enough to have carried out repair work fairly quickly after an earthquake.

If a powerful storm had sunk the ships, there would have been major damage to walls and buildings in the city, but not as much as an earthquake would have caused.

Solution

Passage Analysis:

Text from Passage	Analysis
Excavation in City Y found ten ships that all sank at the same time in the city's harbor, in one sudden event in approximately A.D. 800.	What it says: Ten ships all sank together in one sudden event around A.D. 800 What it does: Sets up the mystery we need to explain - what caused this mass sinking? What it is: Archaeological evidence/factual finding
One possible explanation for the sinking is a tsunami, caused by a strong earthquake from a fault under the sea about fifteen miles away.	What it says: First theory - earthquake caused tsunami that sank the ships What it does: Introduces one potential cause for the mass sinking we just learned about What it is: Author's presentation of possible explanation
However, it is more likely that a powerful storm sank the ships, since, if an earthquake had been responsible, there would also have been major damage to the city's walls and buildings—but there apparently was no such major damage, otherwise we would have discovered records from that time mentioning major building repairs.	What it says: Storm theory is more likely because earthquake would have damaged city buildings, but we found no repair records What it does: Argues against the earthquake theory and supports storm theory using evidence about missing building damage What it is: Author's main argument with reasoning Visualization: Earthquake scenario: Ships sunk + City buildings damaged + Repair records exist → But we only see ships sunk, no building damage records

Argument Flow:

The argument starts with archaeological evidence of a mass ship sinking, presents two possible explanations (earthquake/tsunami vs storm), then argues for the storm explanation by showing what should have happened if an earthquake occurred (building damage and repair records) but didn't happen.

Main Conclusion:

A powerful storm, rather than an earthquake-caused tsunami, is more likely responsible for sinking the ten ships in City Y's harbor around A.D. 800.

Logical Structure:

The argument uses elimination reasoning - it rules out the earthquake theory by showing that an earthquake would have created additional evidence (building damage and repair records) that we don't find, making the storm theory more probable by process of elimination.

Prethinking:

Question type:

Assumption - We need to find what the argument takes for granted but doesn't explicitly state. The argument concludes that a storm (not earthquake) sank the ships because there's no evidence of building damage that would come with an earthquake.

Precision of Claims

The argument makes claims about what would happen (earthquake would damage buildings), what we would find (repair records), and what we actually found (no such records). The precision depends on assumptions about detection, recording, and preservation of evidence.

Strategy

Look for gaps in the reasoning chain. The argument says: no building damage records exist → earthquake didn't happen → storm more likely. We need to identify what must be true for this logic to work. Focus on assumptions about how we detect damage, whether records would exist, and whether absence of records means absence of damage.

Answer Choices Explained

There is evidence that the fault in question had produced tsunamis earlier in City Y's history.

This focuses on whether the fault had caused tsunamis before in City Y's history. While this might be relevant context, the argument doesn't depend on this assumption. The argument is comparing what we'd expect to find from an earthquake versus what we actually found, regardless of the fault's historical activity. The reasoning works whether this was the fault's first tsunami or its hundredth.

Some record-keeping practices existed in City Y around A.D. 800.

This is exactly what the argument must assume. The entire reasoning chain depends on the idea that if major building damage had occurred, we would have found records of repairs. But this logic only works if people were actually keeping records around A.D. 800 in the first place. If no record-keeping practices existed, then the absence of repair records tells us nothing about whether earthquake damage occurred. Without this assumption, the argument's conclusion completely falls apart.

City Y's harbor offered relatively good protection for ships from the effects of a storm.

This suggests the harbor provided good storm protection, which would actually weaken the storm theory rather than support the argument's reasoning. The argument doesn't need to assume anything about the harbor's protective qualities - it's simply using the absence of building damage records to argue against the earthquake theory.

City Y was wealthy enough to have carried out repair work fairly quickly after an earthquake.

This deals with the city's wealth and ability to carry out repairs quickly. However, the argument's logic doesn't depend on the speed of repairs - it depends on whether repairs would have been recorded at all. Even if repairs took years due to lack of wealth, we'd still expect to find some records of the damage and eventual repairs if record-keeping practices existed.

If a powerful storm had sunk the ships, there would have been major damage to walls and buildings in the city, but not as much as an earthquake would have caused.

This makes claims about comparative damage between storms and earthquakes. The argument doesn't need to assume anything about how much damage a storm would cause relative to an earthquake. The argument simply uses the absence of earthquake-related building damage as evidence against the earthquake theory, without making comparative damage claims.

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