What is the displacement of a nascar stock car after he completes the indianapolis 500?
a. 0 miles
b. 500 miles
c. 500 meters
d. 500 seconds

I'm such a devoted NASCAR fan that I don't even know if the starting line and finish line at Indy are the same line ... or maybe they're in different places, like the 100-meter sprint in track.

I have no idea, but I'm going to guess that the start and finish at Indy are the SAME line.  

If that's true, then the displacement of a car that runs the whole 500 miles is very close to ZERO.

Displacement is the distance and direction between the place where the object starts out and the place where it ends up.  The route it follows to get from the start to the finish is completely ignored, and doesn't matter.

(Do they the Indianapolis 500 in "stock" cars ? ?)

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.