I couldn’t find any satisfactory answer. I do not wish to challenge
other’s answer but here is what i think.
when the seek distance is less we need less time to travel,
when it is more we naturally need more time to travel.
The question asks why doesn’t the time change w.r.t. distance.
Inertia and all is good but thinking naturally the time should vary unless we
do some optimization like increasing our speed for travelling far and
decreasing our speed for travelling less, so that we can keep avg. time constant,
or maybe some special scheduling algorithm for special cases.
So i think d should be the answer. Please help and provide some source.