What is the correct meshing condition for a pair of involute helical gears?

A、mn1=mn2=m,αn1=αn2=α,β1=-β2;
B、mn1=mn2=m,αn1=αn2=α,β1=β2;
C、mn1=mn2=m,αn1=αn2=α;
D、Noneoftheaboveoptions