Answer:
speed
Explanation:
In a distance-time graph:
Distance is the y-variable (dependent)
Time is the x-variable (independent)
The slope of a line is rise/run, or can also be calculated with this equation, where "m" is slope:
slope = y-variables / x-variables
slope = distance / time
If you divide distance by the time it took to get that far, you will find how fast you got there. This is called the speed.
You might also see this formula:
k = d/t
In the options, "time" and "distance" would not make sense, because those are the variables on the x-axis and y-axis.