A flare (or arresting of the sink rate) can't be initiated before the threshold / overrun area / displaced threshold because of say any protruding equipment such as light poles. That's why they included option 'c' as a trick answer, where aiming short is dangerous.
If the high sink-rate flare were to start at the same height / location and take the same duration as a normal flare, then the rapid increase in pitch would increase the angle-of-attack considerably and risk (or even cause) a stall. Resulting in 'a', which should not be the technique.
So the flare needs to be more gradual and to start higher, eating up more runway, answer 'b'.
(Own work) No overrun area or displaced threshold to benefit from.
a. same flare location / height, hard landing, risky technique
b. flare higher and more gradually, landing longer ✔
c. aiming short for same spot landing, risk of landing too short
(YouTube) Airbus A318 performs steep approaches—Vref is normal during this ~6° steep approach test / technique demonstration.
See how high the custom callout, "Standby... Standby... Flare," is commanded. Do note the overrun area at London City (first landing in the video), if it weren't there the landing would have been longer.