"which" referent ambiguity

[redexpo]

This is related to GMAT prep explanations for multiple questions. For example, something like "the machines rode around and took pictures, which were helpful in determining the quality of the sample." GMAT prep explanations keep emphasizing that "which" is ambiguous in these cases. But, from reading MGMAT SC guide, I remember quite vividly that if you follow grammar rules, "which" has to modify the noun phrase immediately preceding it, so there is no ambiguity in this construction. Did GMAC change trajectory on "which," or are GMAT prep explanations flawed? Thanks.

[Sage Pearce-Higgins]

Which "GMAT Prep" explanations are you referring to? The GMAT Prep software doesn't provide explanations, as far as I'm aware.

[redexpo]

I am referring to the OG questions in Wiley.

[Sage Pearce-Higgins]

Got it. These are problems from the Official Guide, not the GMAT Prep software. You're right not to trust these explanations, as they contain lots of contradictions and inconsistencies. On the subject of 'which', it's a noun modifier which should be placed as close as possible to the noun that it's modifying. I can't really comment on the example you cite without seeing the full problem (and our rules don't allow you to post it here, as it's copyright). You'll find an explanation in the Navigator software that might help you.