Which root we found 2 canals - Root with 2 canals.. mesial root of upper first molar

Which root we found 2 canals:

OR

Root with 2 canals:

A. distal root of upper molar 

B. distal root of lower molar

C. mesial root of upper first molar ***

D. mesiobuccal of lower

Mesial root of upper 1st molar (most commonly) 

Distal root of lower 1st molar