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The population of Songbirds throughout England has decreased in recent years. Many people explain this decrease as the result of an increase during the same period in the population of Magpies, which eat the eggs and chicks of Songbirds.
Which one of the following, if true, argues most strongly against the explanation reported in the passage?
A- Official records of the population of birds in England have been kept for only the past 30 years.
B- The number of eggs laid yearly by a female Songbird varies widely according to Songbird's species.
C- Although the overall population of magpies has increased, in most areas of England in which the Songbird population has decreased, the number of Magpies has remained stable.
D- The population of Magpies has increased because farmers no longer shoot or trap Magpies to any great extent, though farmers still consider Magpies to be pests.
E- Although magpies eat the eggs and chicks of Songbirds, Magpies' diets consist of a wide variety of other foods as well.
Although, it is a bit oddly worded, this is a rather standard weaken question. First, identify the conclusion as:
Many people explain this decrease as the result of an increase during the same period in the population of MagpiesThe supporting evidence is that "the population of Songbirds has decreased throughout England", and Magpies, the population of which has increased during the same time period, "eat the eggs and chicks of Songbirds".
This is a standard causality argument, positing that there is only one cause for the population decrease of Songbirds, the concurrent increase in Magpies which eat Songbird eggs and chicks. To weaken this argument, it is necessary to provide an alternate cause or show that the two phenomenon are merely coincidental.
A- Official records over the past 30 years are not relevant to the causation between Magpie and Songbird populations, so eliminate choice A.
B- The number of eggs is a vague qualifier that cannot clearly affect the causation between Magpie and Songbird populations, so eliminate choice B.
C- If "the number of Magpies has remained stable in most areas of England in which the Songbird population has decreased", then it is unlikely that the Magpies are in fact the cause of the decrease in the Songbird population, and thus weakening the argument, so keep choice C.
D- The considerations of farmers are not relevant to the causation between Magpie and Songbird populations, so eliminate choice D.
E- The wide variety of other foods in a Magpies diet is a vague qualifier that cannot clearly affect the causation between Magpie and Songbird populations, so eliminate choice E.
The correct answer is choice C.