A flare (or arresting of the sink rate) can't be initiated before the threshold because of any protruding equipment (say light poles). That's why they included option C) as a trick answer.

If the high sink-rate flare were to take the same duration as a normal flare, the sudden increase in pitch would increase the AoA considerably and risk (or even cause) a stall.

So the flare needs to be more gradual and to start higher, eating up more runway.