Thanks for the PM invite to discuss, Atul - it looks like Stuart has this question pretty well under control (so thanks, Stuart!), but if I can add something it's this:
Note that the correct answer in this question actually does use "considered to be". Even though it's probably not a "perfect" idiom, the standard for obscure-idiomatic-correctness is a tough one. If you Google "considered to be" you end up with this link at #1:
https://ethnicity.rutgers.edu/~jlynch/Writing/c.html It calls the "to be" in there "almost always useless"...but doesn't rule it out as flat-out wrong.
Similarly, in regard to the other thread we've been discussing today (
https://www.beatthegmat.com/fusion-t81403.html), there the correct answer uses the idiom "rather than" in the correct answer and not "instead of" (fusion merges atoms rather than splitting them apart). But, again, if you Google "instead of rather than", the #1 link (a GMAT site, actually:
https://gmat-grammar.blocked/2006/0 ... ad-of.html) says that the biggest difference is that "rather than" should accompany preference...and that's can't really be the case with an inanimate scientific process (can fusion really "prefer" something?).
My point - and hopefully I'm not entirely hijacking this thread - is that the GMAT must be an objective assessment of problem solving / logic / critical thinking abilities, and a lot of these idioms are far from objective. Things like subject-verb agreement, pronoun agreement, logical modifiers, logical meaning - these are much more 'it's right or it's wrong' with a definite reason. But a lot of the idioms I see people discussing on here don't have that purity of correctness - there's a preferred way to say something but the less-preferred way isn't always flat-out wrong. "Idiomatic" is a catchall grammatical phrase for "that's just the way it is", and especially now that the GMAT is a global test with examinees who have learned English the American way; the British way; the South African way; the Australian way; and all kinds of hybrid ways, idioms just don't tend to lend themselves to objective assessment...as you can see in these two threads today in which the lesser-preferred idiom happened to be correct.
So if I can try to add some value here, my strong recommendation to everyone here is to focus on the decision points that have a reason behind them: logical agreement, numerical agreement, etc. Those thought processes are replicable, they're objective, they allow you to study fewer "things" and therefore improve or perfect them more thoroughly. And, ultimately, they're the only decision methods that really fit the GMAT's mission to to supply business schools with critical thinkers and problem solvers. If an idiomatic decision point requires you to Google that phrase and consult a dozen or so grammar pages to get to a point where you're 70% sure that one way is preferred over the other, it's a terrible test item...and the GMAT is a sophisticated and well-researched enough test that it's not going to have too many of those.