Which full report correctly avoids backshift after a present reporting verb in the when-not-to-backshift contrast? Direct current warning from the ranger: "The north trail is slippery."

توضیح

Is slippery correctly preserves the present tense after says because the ranger is issuing a current warning. Was slippery and had been slippery relocate the danger to the past, while would be slippery changes it into a prediction.