Access to and Instrumentation on the Lingual Aspect of No

Access to and instrumentation on the lingual aspect of No. 30 and No. 31 is complicated by what anatomic feature?

A) Mandibular posterior crowns are inclined more toward the lingual than the roots, making access more difficult.
B) Mandibular posterior crowns are inclined more toward the facial than the roots making access more difficult.
C) The mandibular first molar mesial furcal concavity makes access more difficult.
D) The mandibular second molar mesial concavity makes access more difficult.