HURT - ?
FILE - ?
BILE - ?
IF FILE = 0, ??R? is proved by score change from FIRE - 1 -> FILE - 0
IF BILE = 0, ?UR? is proved.
FURS - 2 (F disproved by FOLD - 0)
BURN - 2 (B disproved by BILE - 0)
Because there is no score change from ?URN to ?URS, ???N and ???S must both be incorrect, leaving ?UR? - 2