Final answer:
Fire patterns, not debris, charring, or a flashover, are what investigators use to trace how a fire has spread, revealing the origin and path of the fire.
Step-by-step explanation:
The concept of fire pattern is what can trace how a fire spread. Fire patterns are distinct markings created by the fire as it burns, which can provide information on the origin and trajectory of the fire. Investigators observe various details such as charring and the direction of the burn to understand the spread.
On a landscape scale, patterns can demonstrate how topography, vegetation, and meteorological conditions influence the spread of wildfires. While options like debris and charring provide hints, it is the overall fire pattern that gives the most comprehensive information about the fire’s progression.