63.下顎第一大臼齒，依據水平骨性吸收（H）與垂直性骨吸收（V）的程度，下列何者屬於根叉侵犯Class II，subclass B？
(A)H= 0 mm；V= 1～3mm
(B)H= 2 mm；V= 4～6mm
(C)H= 3 mm, not through and through；V= 4～6mm
(D)H= through and through；V≧7mm