## #6 - As far as we know, Earth is the only planet on which

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Complete Question Explanation

Strengthen-PR. The correct answer choice is (E)

The stimulus argues that even though life could exist in non-carbon form on planets very different from Earth, we should still calculate the probability of extraterrestrial life on the basis of the likelihood of carbon-based life in Earthlike situations.

The stimulus proposes a fairly rational means of dealing with the unknown, and does not assert that the probabilities will be correct or that there cannot be non-carbon based life. The stimulus is simply based on the idea that, when addressing the unknown, one should be very conservative and try to make initial projections on the basis of things we understand fairly well rather than on things we have not seen.

You are asked to identify the supporting principle, so you should focus on the idea of selecting a conservative strategy.

Answer choice (A): The argument actually acknowledges that unobserved phenomena may not resemble observed phenomena, but then argues that we should not proceed on that basis, so this choice represents a principle that the argument acknowledges but does not use, and is incorrect.

Answer choice (B): Since the stimulus is only about projecting probabilities and has nothing to do with explaining events, this choice is totally irrelevant and incorrect. Furthermore, the stimulus focuses on a limited area, and so is clearly not based on the principle that one should have a broader focus.

Answer choice (C): This choice is very similar to the supporting principle, but has a fatal flaw. This response asserts that scientists should restrict their studies to the observable, but the stimulus does not need any such principle. The stimulus is concerned with probability estimates, not with what the scientists study. Furthermore in that detail this response is somewhat contradictory to the stimulus, because estimating the probability of life on other planets does involve estimates of the currently unobservable.

Answer choice (D): Since the stimulus concerns estimates of probability rather than actually explaining anything, this choice is wrong.

Answer choice (E): This is the correct answer choice. The stimulus is based on the principle that estimates should be made on a conservative basis, focusing on things similar to the known (carbon-based life and Earthlike planets) rather than fantasizing about the unknown.