chidcguy wrote:Can you tell me what do you mean by a restrictive clause?
I picked B because the sentence reads clearly
we were caught in the middle of the crisis in education created by the Soviet Union’s “Sputnik” success
with out the middle phrase
A restrtive clause (or phrase) is information that is necessary to understand the sentence. Most commonly, the GMAT uses "that" to begin a restrictive phrase.
A non-restrictive phrase is "bonus" information that's not necessary to understand the sentence. Most commonly, the GMAT uses "which" to begin a non-restrictive phrase, which will appear between commas.
Here are two examples:
"Law 461, which governs gun control, is up for review."
We already know that we're talking about Law 461, so "which governs gun control" is just bonus description - non-restrictive.
"The law that governs gun control is up for review."
Well, "the law" doesn't tell us enough to understand what the author is discussing. So, "governs gun control" is necessary to understand the sentence - restrictive.