Summary judgment is proper only when no genuine issue of material fact exists and the moving party is entitled to judgment as a matter of law. Rule 56(c), M.R.Civ.P. In a negligence case, a plaintiff must prove the following elements: (1) duty; (2) breach of that duty; (3) causation; (4) damages. Wiley v. City of Glendive, 272 Mont. 213, 217, 900 P.2d 310, 312 (1995). If the plaintiff fails to offer proof which establishes any one of those elements, summary judgment is appropriate. Singleton v. L.P. Anderson Supply Co., Inc., 284 Mont. 40, 44, 943 P.2d 268, 270 (1997). The existence of a duty is a question of law. Estate of Strever v. Cline, 278 Mont. 165, 171, 924 P.2d 666, 669 (1996).