A store owner exercises ordinary care by making reasonable inspections of the portions of the premises open to customers. (Ortega v. Kmart Corp., supra, 26 Cal.4th at p. 1205, 114 Cal.Rptr.2d 470, 36 P.3d 11.) The care required is commensurate with the risks involved. (Ibid.) Thus, for example, if the owner operates a self-service grocery store, where customers are invited to inspect, remove, and replace goods on shelves, the exercise of ordinary care may require the owner to take greater precautions and make more frequent inspections than would otherwise be needed. The owner must safeguard against the possibility that such a customer may create a dangerous condition by disarranging or dropping the merchandise. (Ibid.) “ ‘However, the basic principle to be followed in all these situations is that the owner must use the care required of a reasonably prudent [person] acting under the same circumstances.’ ” (Ibid.).