Happy to help. This is a strengthen question, and we're looking to pick the answer choice with the general principle that would most strongly support the recommendation.
In looking at the stimulus, the author's conclusion is that we should calculate the probability of extraterrestrial life by discovering planets like Earth and then figuring out the probability of the carbon-based life forms on those planets. The author supports this conclusion by offering the evidence that so far, as far as we know, all of the life that we are familiar with is carbon-based.
Since we're looking to strengthen this argument, it might help us to focus on the gap between the premises and the conclusion. In the argument, the gap exists between the knowledge that we have and what we are supposed to search for. Ideally, the answer we pick will provide us with a great reason to suspect that searching for carbon-based life forms is a good way of estimating the probability of extraterrestrial life on other planets.
(E) says, "Estimations of probability that are more closely tied to what is known are preferable to those that are less closely tied to what is known."
In the stimulus, the proposal of the author is to closely tie the estimation of extraterrestrial life to what we know about life on Earth. (E) provides us with a principle that gives us a great reason to adopt the author's proposal, so it's the correct answer choice. It strongly supports the authors' recommendation.
Does this make sense? Let us know if you have any more questions!
