Where Is the Mesial Furcation Usually Located on a Permanent

Where is the mesial furcation usually located on a permanent maxillary first molar?

A) One third of way in from the mesial aspect
B) One third of the way across the distal surface from the buccal aspect
C) Two thirds of the way in from the lingual aspect
D) Two thirds of the way across the mesial surface from the buccal aspect