Logical reasoning PrepTest 156 · Section 2 · Question 14

This hypothesis isn't supported. We hypothesized that the ice caps may have grown over the first 20,000 years, which probably means that the average global temperatures decreased over that period. We also hypothesized that ice caps may have shrunk for the next 10,000 years, which probably means that the average global temperatures increased over that period. So, from year 10,000 of this period, the temperatures probably increased until year 20,000, at which point they decreased until year 30,000. Still, even though the temps go up and down, we can't say that the temperatures at year 10,000 were the same as those at year 30,000 — that's far too specific an inference to draw from this data. We don't know how much the temperatures have to decrease for ice caps to grow or how much the temperatures have to increase for the ice caps to shrink.

This hypothesis isn't supported. We hypothesized that the ice caps may have grown over the first 20,000 years of this period. Even though the ice caps probably shrunk for the last 10,000 years, the caps at the end of this period may still be bigger than they were at the beginning. For instance, if the ice caps grow faster than they shrink, they will almost certainly be larger at the end of this 30,000-year period.

This isn't supported by the facts. Although we hypothesized that the ice caps may have grown over the first 20,000 years of this period, that doesn't necessarily mean there was an ice age during this time. According to the passage, ice ages are just one example of a time when the polar ice caps would grow. There could be other circumstances that would cause the ice caps to grow, and this period could be one of those circumstances. And even if there was an ice age during this period, that doesn't necessarily mean the "onset" of the ice age occurred at the beginning. The ice age could have started before this period began.

This matches our anticipation, even if it's expressed in more certain terms than we were willing to use. Still, this answer choice is the best option we've encountered so far. Unlike (A) through (C), it doesn't make an additional inference that isn't supported

Plus, this question stem asked us for the best "hypothesis" we could form. Hypotheses are explanations that we can test to see if they're false. So, it's probably OK that the wording of this hypothesis is a little too strong. After all, it's a lot easier to prove that a strong statement like "The polar ice caps grew for about 20,000 years after the period began, then began to shrink" is false than a weak statement like "The polar ice caps may have grown for about 20,000 years ..."

So, we'll mark (D) as a strong contender. We'll look at the remaining options to see if any express the same idea as (D) but with weaker language. If none do, we'll select (D) confidently.

This answer choice is wrong for many of the same reasons as (C). Even though we hypothesized that the ice caps may have grown over the first 20,000 years of this period, that doesn't necessarily mean there was an ice age during that time. The passage says that ice ages are an example of a time when the polar ice caps would grow, but other circumstances could cause the ice caps to grow. Moreover, even if there was an ice age during this time, it didn't necessarily draw to a close by the end of the first 20,000 years of this period. We hypothesized that the ice caps may have started shrinking after year 20,000, which probably means the temperatures were increasing during this time. But that doesn't mean the ice age was ending. It could have become a less severe ice age over the last 10,000 years.