Answer:
I think it's D. The independent variable is the length of the race. The dependent variable is the time.
Explanation:
Here I'm quoting user kaylaj051903 "because an independent variable is something that is constant and does not change throughout the problem. The dependent variable depends on the independent variable. The race is a 5K race. That will not change. What will change is how long it takes Stephanie to run the 5K race."