Because ethylene dibromide, a chemical used to fumigate grain, was blamed for the high rate of nerve damage suffered by...
GMAT Critical Reasoning : (CR) Questions
Because ethylene dibromide, a chemical used to fumigate grain, was blamed for the high rate of nerve damage suffered by people who work in grain-processing plants, many such plants switched to other chemical fumigants two years ago. Since then, however, the percentage of workers at these plants who were newly diagnosed with nerve damage has not dropped significantly. Therefore, either ethylene dibromide was wrongly blamed or else the new chemicals also cause nerve damage.
Which of the following is an assumption on which the argument depends?
Passage Analysis:
| Text from Passage | Analysis |
| Because ethylene dibromide, a chemical used to fumigate grain, was blamed for the high rate of nerve damage suffered by people who work in grain-processing plants, many such plants switched to other chemical fumigants two years ago. |
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| Since then, however, the percentage of workers at these plants who were newly diagnosed with nerve damage has not dropped significantly. |
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| Therefore, either ethylene dibromide was wrongly blamed or else the new chemicals also cause nerve damage. |
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Argument Flow:
The argument starts with background information about plants switching chemicals due to nerve damage concerns, then presents the surprising fact that nerve damage rates didn't improve, and finally concludes there are only two possible explanations for this outcome.
Main Conclusion:
Either ethylene dibromide was wrongly blamed for nerve damage, or the new chemicals also cause nerve damage.
Logical Structure:
The author uses the premise that nerve damage rates didn't drop after switching chemicals to conclude that either the original chemical wasn't really the problem, or the replacement chemicals are just as bad. This creates a logical either-or conclusion based on the unexpected results.
Prethinking:
Question type:
Assumption - We need to find what the argument must assume to be true for the conclusion to hold. The conclusion is that either ethylene dibromide was wrongly blamed OR the new chemicals also cause nerve damage.
Precision of Claims
The key claims involve causality (what causes nerve damage), timing (two years since the switch), and measurement (percentage of workers with new diagnoses hasn't dropped significantly). We need to focus on what conditions must be true for this either-or conclusion to be valid.
Strategy
For assumption questions, we identify ways the conclusion could be falsified while respecting the given facts. The argument concludes there are only two explanations for why nerve damage rates didn't drop after switching chemicals. We need to think about what the argument must assume for this limited set of explanations to be complete and valid.
If the new chemicals cause nerve damage, the nerve damage caused would be different from any nerve damage that ethylene dibromide may cause.
'If the new chemicals cause nerve damage, the nerve damage caused would be different from any nerve damage that ethylene dibromide may cause.' This isn't something the argument needs to assume. The argument's conclusion works whether the nerve damage from different chemicals is the same or different. The key issue is whether nerve damage is occurring, not what type of nerve damage it is. The argument doesn't depend on being able to distinguish between different types of nerve damage.
There are no chemical fumigants that are completely safe for workers in grain processing plants.
'There are no chemical fumigants that are completely safe for workers in grain processing plants.' The argument doesn't need to assume this broad claim about all possible fumigants. The argument is specifically comparing ethylene dibromide to the new chemicals that were actually chosen as replacements. Whether completely safe alternatives exist somewhere is irrelevant to the logic of this particular comparison.
If ethylene dibromide causes nerve damage, it does not take two years or longer for that damage to become detectable.
'If ethylene dibromide causes nerve damage, it does not take two years or longer for that damage to become detectable.' This is exactly what the argument must assume. If nerve damage from ethylene dibromide takes more than two years to show up, then the workers currently being diagnosed could still be suffering from pre-switch exposure to ethylene dibromide. In that case, we wouldn't expect to see a drop in nerve damage rates yet, which would undermine the entire either-or conclusion. The argument's logic completely depends on this timing assumption.
Workers at grain-processing plants typically continue to work there even after being diagnosed with nerve damage.
'Workers at grain-processing plants typically continue to work there even after being diagnosed with nerve damage.' This doesn't affect the argument's logic. The argument is about the percentage of workers being newly diagnosed with nerve damage, not about what happens to workers after diagnosis. Whether diagnosed workers stay or leave doesn't impact the rate of new diagnoses in the remaining workforce.
Workers at grain-processing plants that still use ethylene dibromide continue to have a high rate of nerve damage.
'Workers at grain-processing plants that still use ethylene dibromide continue to have a high rate of nerve damage.' The argument doesn't need to assume anything about plants that didn't switch chemicals. The argument is specifically about what happened at the plants that did switch from ethylene dibromide to new chemicals. Information about plants that kept using ethylene dibromide isn't necessary for this argument's conclusion.