Hi shakas,

As a general rule, you're supposed to write and speak in "active voice." There are some circumstances in which "passive voice" is correct, but these are not common on Test Day (you might see 1 or 2 at most). So, if you "narrow it down to 2 and have to guess", here are some general patterns that you can use:

1) The shorter answer tends to be correct
2) Nouns are preferable to pronouns
3) Sophisticated-sounding language is preferable

GMAT assassins aren't born, they're made,
Rich

I think perhaps you've misunderstood the MGMAT advice; the point is that the GMAT can exploit the mentality of "I need a rule for which one to use in every single case!"

You should take active/passive issues on a case-by-case basis. In English, active voice is generally preferred when speaking or writing. This doesn't mean that passive voice is incorrect, though! (In fact, look at the sentence before last: "active voice is preferred" is in the passive voice). Don't use passive/active to eliminate any answer choices until you're considered every other grammar and meaning error in the sentence.

There will be GMAT question with active/passive splits in which the active is preferred, such as OG#16:
Correct: "... claims suggest that the economy might not be as weak as some analysts previously thought."
Incorrect: "... claims suggest that the economy might not be as weak as have been previously thought by some analysts."

Here, though, we could also rule out the incorrect choice based on the incorrect use of "have." Right answers will almost never come down to simply a passive/active distinction.

There are also plenty of times in which the passive voice is necessary or even preferred, such as #90 in the 12th ed. The correct answer states:
"Although soap operas were first aired on evening radio in the 1920's, they were moved to the daytime hours..."
Here, passive voice is not only acceptable, it's necessary! From a meaning perspective, soap operas can't air or move themselves, and we don't know or care who aired/moved them in the context of this sentence.

To your question,

Given the number of concepts tested in SC, does it even occur that active/passive voice is the last concept "alive"?

The answer is that it may happen, but very, very rarely - my guess is that far fewer than 1% of problems will come down to this issue. Try not to dwell on it.

For more on passive/active, see:
https://www.beatthegmat.com/william-shak ... tml#581346
https://www.beatthegmat.com/passive-vs-a ... tml#584446
https://www.beatthegmat.com/difference-b ... tml#577384