The ugly incidents of the Civil War are water under the bridge. This means that the incidents
Answer Details
The phrase "water under the bridge" is an idiom that means something that happened in the past and cannot be changed or undone.
So when we say, "The ugly incidents of the Civil War are water under the bridge," it means that those incidents are in the past and cannot be changed. It implies that they have been forgotten, and we should not dwell on them or let them continue to affect us.
Therefore, the correct option is "have been forgotten." The other options do not fit the context of the sentence. The sentence suggests that we should move on from the past and not let it continue to affect us. It does not suggest that the incidents are still haunting us, have been experienced again, or cannot be wished away.