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Over the last few years, Country A has suffered a pest infestation which has resulted in huge losses in agricultural yield. Since the infestation began, Country A’s imports have increased. Therefore, Country A will continue to import more than it did before the infestation started, and this will remain so until the infestation ends.

Remember we identified the components of this passage in the introductory article on argument-based passages. Now let us suppose that this passage appeared in your test with the following question-stem and possible answer choices:

Question: The argument in the passage is based on which of the following assumptions?
A. The economy of Country A traditionally relies on its agricultural exports.
B. The rural populace of Country A is generally agreeable to the idea of importing agricultural products.
C. The infestations have affected every type of crop.
D. The increase in imports is caused by the losses in agricultural yield.
E. A significant proportion of the recent infestation in Country A is caused by the boll weevil pest.

Now if you recall the conclusion of the above passage:
Conclusion: Country A will continue to important more than it did before the infestation started, and this will remain so until the infestation ends.
The author reached this conclusion from the premises that Country A has incurred major losses in agricultural yield due to infestation, and that since the infestation began, an increase in imports has already been observed. In other words, the author is trying to argue that since the increase in imports coincides with the losses in yield due to infestation, it must therefore have been caused by and, by extension, end with the infestation itself.
To identify the assumption on which this passage is based, we have to ask ourselves the vital question “What is that one general fact on which the validity of this whole argument depends?” In other words, the right answer choice is the one that should be absolutely true for the conclusion to be true. Without assuming that unstated general fact, the whole argument falls apart.
There is one sure way of identifying this all-important assumption on which the passage rests. Since the assumption has to be true for the conclusion to be true, start negating every answer choice one by one and see what bearing it has on the conclusion of the argument. If negating an answer choice does not affect the conclusion then it is not the assumption we’re looking for. Negating the right assumption will render the conclusion wrong and the argument invalid. Let’s evaluate the answer choices to see which one of them is the assumption on which the argument is based.

Answer choice A states that the economy of Country A traditionally relies on its agricultural exports. To see if it is the required assumption, let’s negate it and see if it invalidates the argument. Even if we assume the opposite i.e. the economy does not rely on agricultural exports, the conclusion (i.e. increased imports will continue for as long as the infestation continues) still remains intact. Dependence of economy on agricultural exports has no bearing on a prediction that concerns imports. Hence this answer choice does not act as a necessary assumption on which the argument rests. In fact the opposite may be argued that over-dependence on agricultural exports would mean that in a time of crisis Country A will not have the necessary revenue to buy anything from other countries (although this line of reasoning is also unfounded since it assumes outside information i.e. the country did not have any surplus revenue in treasury or that it cannot acquire the necessary revenue from other sources).

Answer choice B states that the rural population of country A is acquiescent to the idea of importing agricultural items. This is a very tempting answer choice, since one may be falsely led to assume that governments always and only implement an idea if the population is amenable to that idea. Even with this unwarranted outside assumption, for this option to be correct we will have to further assume that the rural population will continue to be agreeable to the idea of import for as long as infestation continues. Anyhow, let’s use the method of negation on this answer choice. Let’s assume for a second that the general rural population is loath to the idea of import. Does it necessarily bar the government of Country A from continuing to import more until the infestation ends? No, hence the conclusion remains intact. Therefore this option is clearly not the assumption on which the argument in the passage rests.

Answer choice C only further elaborates the point that Country A has incurred considerable losses due to infestation by stating that the infestation has affected every type of crop. However, it is not the assumption on which the argument rests. Let’s verify by negating the option: infestation has not affected every crop type. Does it mean that Country A will not continue to import more until the infestation ends? Not necessarily, and hence the conclusion remains intact.

Answer choice D is correct. It states that the cause of increase in imports is the losses in agricultural yield. We already know from the passage that infestations are directly responsible for these losses. Hence a proper chain of causations has been established by this answer choice which is absolutely vital for the conclusion to be true. Let’s verify using the method of negation by supposing for a moment that increased imports are NOT caused by agricultural losses. That would imply that there is some other cause for this increase in imports which is not tied to the recent infestations. That would render the conclusion (that the increased imports will continue as long as the infestation continues) unfounded and invalid. Hence option D is the assumption on which the argument in the passage is based.

Answer choice E only specifies one of the pests involved in the infestation. Needless to say, it is irrelevant to the conclusion.

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