A modifier can be understood in two ways

[ZimingY929]

In the latest correction of SC GMAT Strategy Guide 6th edition, on page 37, the answer of the sencond question is "Solutions, #2: The correct answer is B, not C. The explanation should be as follows: '(B): In the original sentence, the modifier who had been waiting does not clearly modify the people. It appears, illogically, to modify the closer noun (the airport). The boldface version moves who had been waiting next to the people, thus making clear that it is the people who had been waiting.' ”https://www.manhattanprep.com/gmat/errata/errata-sc-6ed/
But in my opinion, the bold vesion can also lead to ambiguity, because applying the bold vesion the whole sentence is " The driver picked up the people who had been waiting at the airport ". Now, is the " at the airport" a modifier of " waiting" or a modifier of " picked up"? With all due respect of the editors of the book, I believe this is surely an ambiguity. So I look forward to an official instructor to explain this issue: is it a real mistake or I misunderstood something.
Thx to all people willing to contribute to this issue.

[StaceyKoprince]

Hello! This folder is only for general strategy questions, not content or specific test problems. Check out the content / problem folders and post in the relevant folder depending upon the source of the material that you want to post (and make sure to follow the rules about banned sources).

Note: All of the content folders are viewable to the public but only our students can post in them.

(Short answer: That sentence is correct as written. At the airport modifies waiting. Where were they waiting? At the airport. Separately—logically, they were picked up where they had been waiting to be picked up.)