The question on Polio that I cited in my article is actually from OG VR2 Q36 and the correct option uses the reduced form. The explanation given in OG VR2 for correct option E says:
Indeed we reduce adverbial clauses for concision.
"The Official Guide explanations have been created by different teams over the years – some explanations are from ETS (which administered the GMAT pre-2005); some explanations are from a 3rd party to whom GMAC outsourced the work, and some explanations are created by GMAC experts themselves (hopefully the best ones!). This explains the discrepancy in the quality of answers provided to the awesome questions in the OG."
And this explains the inconsistency among different explanations for the same concept.
tarunktuteja
Thanks tarunktuteja for your help,
Actually I knew those stuff about reduction of adverb clauses.
But the point is the GMAT's inconsistency about usage of 'although' with or without a verb and subject; as I have pointed out, GMAT in one other case, i.e. page 739 of OG2015, in the explanation for choice D of question 74, asserts that:
"Although is a conjunction and should be followed by a finite clause with a subject, not by a participle."
If this is GMAT's position (about how 'although' (and similar subordinating conjunctions) should be used), then '
although eradicated in the United States' should also be wrong, since in this case 'although' is followed by a participle, i.e. 'eradicated', rather than a S-V.
Do you have any idea how this inconsistency can be solved?