A dangling modifier is a phrase or clause that is not clearly or logically related to the word or words it modifies. The sentence "Still surviving today, the ancient Romans built many stone arch bridges" has a dangling modifier, because it seems like the ancient Romans are still surviving instead of the stone arch bridges. The correct revision is letter B, "The ancient Romans built many stone arch bridges that still survive today." In this sentence it is clear that the writer is saying that the stone arch bridges still survive and not the ancient Romans. Revisions A, C, and D do not make sense as they still suggest the ancient Romans still survive.