Looks like there's a bit of confusion on this one, so I thought I'd jump in.
"As rare as something becomes, be it a baseball card or a musical recording or a postage stamp, the more avidly it is sought by collectors."
The preposition "as" has a lot of uses, but they are not infinite.
We can use it to express something about time: "As the world turns, everybody gets older." We can use it for expressing equivalency between two things: "I am as strong as you are." We can also use it to compare clauses "Just as swimming is good exercise, so is croquet."
Finally, the example that comes closest to this question, is the use of "as" to set up a contrast: "As much as I like Dave, I can't stand to hang out with his girlfriend." In this version, the first clause is set up as a contrast with the second.
None of these match up with this sentence. A reword could get us the first example I used, "As something becomes more rare, it becomes more valuable." But that's not how they wrote it.
The issue here is one of parallelism/contrast. The best way to write this sentence is to have a correct parallel to "the more avidly it is sought". "As rare" doesn't match at all. "The rarer something becomes" matches perfectly. Both have a comparative ("more avidly" and "rarer), followed by a verb. Watch:
The more avidly it is sought
The rarer something becomes
(A) As rare as something becomes, be it
PROBLEM: See above.
(B) As rare as something becomes, whether it is
PROBLEM: See above.
(C) As something becomes rarer and rarer, like
PROBLEM: "Like" is used to compare nouns, "such as" gives examples. We definitely couldn't use like here, because there's no noun in the first clause to actually compare it to (aside from "something", but how can you compare to "something"?).
(D) The rarer something becomes, like
PROBLEM: Same as in C.
(E) The rarer something becomes, whether it is
Hope that helps!
Tommy Wallach | Manhattan GMAT Instructor | San Francisco
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