Hi, there. I'm happy to help with this.
You're right --- as the sentence currently is written, the participial phrase "fashioned either from the spotted sandstone of mathura or gandharan grey schist
" modifies "Kushan Empire
," which is incorrect. This is a misplaced modifier.
Adding a comma does not eliminate the glaring mistake of a misplaced modifier. The only way to get rid of a misplaced modifier problem is to reconstruct the sentence. Commas do not work magic. Commas do not make bad grammar go away.
You will notice, with this particular question (SC #56 in the OG 12e), the OA of E transforms this participial phrase into a full-fledged verb that is parallel to the first verb ---- the structure of the sentence has been entirely altered, to eliminate the misplaced modifier problem.
Does all this make sense?
Here's another SC question drawing on the modifier touch rule. http://gmat.magoosh.com/questions/1174
When you submit your answer, the next page will have a full video explanation.
Let me know if you have any further questions.
Magoosh Test Prep