Solutional caves are formed in the earth when a soft rock, usually lim

Official Explanation

Reading the question: We have a brief argument, so we can use term matching.



There is an assumed relationship between "formed from" and "surrounded by." In short, the argument says that Troglotopia Cave wasn't formed from soft rock because it's not surrounded by soft rock. We'll filter for answer choices that relate these two concepts.

Applying the filter: choice (B) matches our filter, because it basically asks whether the formation process means there will be no surrounding soft rock, so it connects "formed from" and "surrounded by."

Logical proof: as the "whether" words hint, we can logically prove that (B) is correct and the other answer choices are incorrect through analysis by extreme cases. In (B), if the cave formation always erode all surrounding soft rock, then the conclusion of the argument is incorrect. On the other hand, if the cave formation never erodes all surrounding soft rock, then the conclusion of the argument is correct. So we have found that the correctness of the argument depends on (B). We don't get a similar result for analysis by cases in the other answer choices. In the case of choice (D), for example, we can imagine that Troglotopia Cave has a shape that highly resembles other solutional caves or that it has a very different shape. The argument is unaffected by these considerations, because the argument does not draw on the shape of the cave as evidence. Most of the other answer choices have the wrong focus, which is on carbonic acid, which isn't central to the evidence or conclusion.

The correct answer is (B).

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