Which of the following is a natural reference for navigation?

In the context of underwater navigation, natural references are typically features or indicators found in the environment that divers can use to orient themselves and navigate effectively. Light and shadow fall into this category as they are inherent characteristics of the underwater landscape.

Light can create patterns and variations in visibility caused by the angle of the sun, water clarity, and the surrounding environment. Divers can use the position of light to determine which direction they are facing or where they need to go. For example, during the day, the sun's position can provide a directional cue, while shadows can indicate structures or changes in depth or terrain.

Using water temperature, surface buoy markers, or dive time does not qualify as a natural reference in the same sense. Water temperature tends to be consistent in a given area and does not give a diver directional cues. Surface buoy markers are artificial aids to navigation, not natural, and dive time relates more to timing and planning rather than actual geographic orientation.