Thanks shimbal80, Tani, and lunarpower! Great thread.
Seeing questions side by side -- and studying variations of questions -- is always instructive.
Looking at the answer choices to these questions, you see there is actually a difference: in the latter question, C) and E) have the additional word "of." This difference is telling. The "explosion" is not "a type" - rather, it is OF a type. Things and types of that thing cannot be identical. The error in answer choice A), which lacks the word "of," is similar to the comparison errors we see in many SC questions. For this reason, we're able to choose E) over A) without even having to consider which side wins in the battle of "to be" vs. "is."
The first question posted doesn't have any mention of "types," so the decision between A) and E) is more difficult in this question. While the questions are very similar, they hinge primarily on different choices. I'd have chosen E) in a blink without being able to define why. I'd note that E) is a more concise expression, regardless of actual word count. Also I think that E) more properly conveys the fact that the clause that comes afterward does not so much define the ecosystem (a task restrictive "that" clauses do better), but rather equate it was something that it is, well, believed to be
-- a task that the idiom "believe to be" does precisely.
Side note: if that last explanation seems esoteric to you, I'll point out that the key arbiter of whether a question is a proper test item is the response data. The method that GMAC uses to gauge question fairness (a method we attempt to emulate) is to compare response curves for particular questions against the general performance of those individuals. We pay more attention to these patterns in our CAT pool than our Quiz Bank, but we'll take a look. When practicing SC questions, I would focus on doing many questions, absorbing the patterns, and etching each question into your memory.
Is that helpful, shimbal80? If you still have questions feel free to hit me with a PM.
-andrew
