SC: A synthetic polymer is used in airbags

[MohitS94]

A synthetic polymer is used in airbags because it is not as tough as to cause injury or as weak as to tear during an impact.

(A) as tough as to cause injury or as weak as to tear
(B) so tough that it causes injury or so weak that it could tear

Is the idiom as...as to in (A) incorrect?

And would so tough as to... be more appropriate in (B)?

OA is (B) and I'm not trying to challenge it. Just wanted to know an instructor's opinion on the idiom.

Source: I had to make this question up, since the actual question is from the GMATPrep paid exam pack. All the words are different and I've changed the original sentence. That is also why there are only two options. The other options violated parallelism and it felt pointless to "translate" them to my new question. I apologise for the post if all this still makes it illegal to post here.

[RonPurewal]

in the context of your version, B doesn't really make sense.

in this context, both verbs represent hypotheticals (= things that could happen during an imagined impact). so, you'd want a sentence with "...could cause injury ... could tear".

you may want to try again, this time making a greater effort to create a version that preserves the tense relationships of the original.

[RonPurewal]

Is the idiom as...as to in (A) incorrect?

yeah, that's not a thing.

you could write "so tough as to ...", but not that.

[MohitS94]

Hi Ron,
I found the original question here:
http://www.beatthegmat.com/road-t83192.html

Could you please have a look at option (A) there?
That is similar to my option (B).

And thanks for clearing up that idiom.

[RonPurewal]

ah, ok. so, it's similar... but not similar enough.
(:

consider:
this chemical is unstable and could explode at any moment.

make sure you understand why those tenses aren't the same.
• the chemical is unstable; this is a fact.
• on the other hand, it has the potential to explode, but has not yet done so. thus "could".
• any attempt to write both verbs in the same tense (e.g., ... is unstable and explodes at any moment) will produce nonsense.

the same pattern obtains in the correct choice for the problem you've linked. one verb describes the state in which something exists in general, whereas the other describes a potential event that may or may not actually transpire.

[RonPurewal]

also, if you happen to know the aforementioned idiom, then the linked problem is quite straightforward. B, C, E suffer from non-parallelism, and D uses the same unidiomatic structure twice.

if you don't know the idiom, then you can still solve the problem by thinking carefully about the tenses, as described above.

[MohitS94]

Thanks Ron. It's pretty clear now why the tenses were different in the OA.

[RonPurewal]

excellent.