CAT Critical Reasoning Practice question with Solution 63

The author concludes that environmentalists are wrong to worry about increased carbon levels due to the burning of fossil fuels, because nature will continually adjust the carbon level. However, if, as choice (E) states, the adjustment process works very slowly, allowing wide short-term fluctuations in the carbon level, then it’s conceivable that dangerous or even lethal levels of carbon can build up, thus severely weakening the author's argument: the environmentalists would be right to worry.

(A), (C) The author doesn’t debate the necessity of carbon, she merely argues that nature takes care of the carbon level by itself, and that the environmentalists should chill.

(B) Some may feel that this weakens the author’s concession in the last sentence, but even if it did, that sentence is basically a tangential point that has little to do with the logic of the argument, which deals with nature’s regulation of the carbon level. However, this probably doesn’t even affect the author’s concession, because that statement never said or implied that the threat to humans of increased carbon levels would come from breathing it in; it would likely be more indirect, along the lines of the processes described.

(D) This is an irrelevant comparison that has no bearing on the logic of the argument.

Recognize filler material (like the author’s concession that a sustained increase in the carbon level would threaten human life) that plays no real part in the overall logic of the argument. There’s usually a wrong choice that keys off of such irrelevant info.