I think DP's answer was the correct exam question answer.
I use time as the reference...and plan my ROD.......so if I need to lose 10'000feet and I
want a 500fpm ROD I'll start my descent 20 mins out. How far out you are depends on your speed of course. At 120kts this is 40nm, 240kts 80 miles.
Or I setup the VNAV profile on the GPS
