Ziyuen, +1 for identifying the source of the question! LSAT used to license their questions to GMAT test-prep companies, but they stopped doing that a year or two ago, interestingly.

Anyway, on to your question. There are plenty of pretty good explanations already on this thread, so I'm not going to rehash all of them here -- but I do think that Tommy Wallach's explanation is spot-on, though I guess he could have said more about (E).

Remember that in an assumption question, you're looking for something that's necessary to draw the conclusion. It might not be 100% satisfying, or 100% airtight. It may not be the ONLY thing you need to draw the conclusion. But without it, the conclusion wouldn't work.

So... (E):



This sounds nice and everything, but you definitely don't want to confuse "enthusiasm on the part of a potential audience" with an explosion in the actual audience. It's fine if the 45 companies were founded when potential audience members were excited, but that does nothing to convince us that there has been a real explosion "of public interest in, and enjoyment of, opera over the past three decades." The enthusiasm (of a merely "potential" audience) when the companies were founded has little to do with any "explosion" of general public interest over a period of 30 years.

More importantly, (E) simply isn't necessary. You don't need to know anything about the enthusiasm levels when the companies were founded in order to show that there's been an explosion in public interest in opera. If you assume the opposite -- i.e., that there was little enthusiasm when the companies started -- it would still be possible that there was an explosion of interest later. (Real example: Starbucks was founded in 1971. Nobody gave a crap until the mid-1990s.)

But (B) is absolutely necessary, as others here have indicated. If the opposite of (B) is true -- that more opera companies closed than opened in the 30-year period -- then the argument falls apart in a big hurry.

I hope this helps!
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