D - I reckon.
You are trying to convert what happens in the air to what happens on the ground - this is done by adding/subtracting the effect of wind.
Mean wind is always used and, as you are looking ahead, surely it is the mean wind up to the next isochrone.
Well, that's the "applying logic" approach, anyway!
BTW - although I pilot, I reckon that having a grade B 'O' level pass in Air Navigation permits me to have Honorary Life Membership of SODCAT.