Hi vlad,
It's always interesting seeing an unusual question on RC like this one and I really enjoyed the concept being tested. They want me to basically define "crucible" (basically, a severe test or process leading to something new) but they want me to find a term in the passage that most resembles that "crucible" term in the passage. So it's a word hunt with contextual reading? This is definitely a situation where I want to sort contenders and losers to make sure that I get the right answer, so let's look at them:
(A) Temptation? I am already suspicious. But even if you don't know what a crucible is, you should know what temptation is, if you are going to sit for the LSAT. And you should know that while temptation can be tested from time-to-time, it's not something that happens between two adversaries. Cross it off.
(B) Credibility? Well, a crucible is not about believing in someone like credibility. But again, that contextual reading of crucible tells me it's a process of the adversarial system. And I don't see much process happening in the term credibility as it is used in the passage. Cross this one off too.
(C) Engine? Well, there is a process to an engine. And it seems like they are really talking about "legal process" in the passage. Hey! This looks pretty good. Especially since it seems like both terms could be replaced with a "test or process" and still read correctly. Contextually, this looks good and if I know the word "crucible," this answer is really cake. Circle this one as a strong contender and check those other two answers quickly.
Function and medium are both so specific here in the other answers. The term "function" as it's used in the passage is really synonymous with "role" and role really does not work when replacing the word crucible. Medium is even worse as it's referring to books or the internet, etc. That's just flat out wrong.
That's why Answer Choice (C) is correct.
Thanks for the great question! As an LSAT nerd, this was fun!