Answer :
I believe its "paul saw a billboard advertising a music festival" :) hope it helped!
Answer:
The answer is B While he was driving on the highway, Paul saw a billboard advertising a music festival.
Explanation:Each modifier should be placed as close as possible to the thing that it is meant to modify. In the original sentence, the modifier "Advertising a music festival" is misplaced. It should be placed after "billboard" since that's what it is meant to modify.