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Critical Reasoning: Investigation Questions

In a recent experiment, a spider breed was chosen as a potential natural pesticide to reduce the numbers of a certain insect that is very harmful specifically to growing watermelons. In an average infested watermelon field, tagged spiders were released, and their feeding monitored for a month. Results of the experiment showed that although the spiders ate extremely well, the number of pests remained the same as the month before. Therefore, the spiders must have eaten other insects and not their intended prey.

Which of the following would it be most useful to establish in order to evaluate the argument?

Incorrect.

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This answer choice asks an irrelevant question. The argument deals with the relationship between the spiders and the pests and does not involve any other predators.

Incorrect.

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The conclusion focuses on the reason for the unchanged number of pests. Therefore, this answer choice about the spiders' effect on the watermelons' state is irrelevant.

Incorrect.

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This comparative figure would be useless. We do not know how many spiders were first introduced to the field. Besides, the argument focuses on the number of pests, not spiders.

Incorrect.

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The answer to this question would not get us any closer to proving or disproving the author's conclusion. Even if there were spiders that preyed on the pests, the field was still considered infested at the start of the experiment.

Superb!

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This answer choice asks a critical question which could shed some light on the argument. If previous population figures of the pest show an increase over time, then a repeat of the population figure is an improvement to the overall situation - the spiders halted the pests' infestation! However, if previous figures show a constant population, then the spiders probably did eat other insects.

Whether the harmful insect is preyed upon by any other predators, be they insects or small creatures
Whether the particular breed of spider chosen also causes harm to watermelons due to its nesting
Whether the number of spiders equalled the number of watermelon pests after one month
Whether the field already contained spiders that perhaps prey upon the watermelon pests
Whether previous population figures for the watermelon pest show an increase over time