The class ___ are obtained when we divide the sums of the lower and upper class limits by 2?

A. 1+ fm – f2/f1 – f2 x h
B. 1+ f1 – f2/f2 – fm x h
C. 1 + fm – f1/ (fm – f1) + (fm1 – f2) x h
D. 1+ fm1 – f2/f1 – fm x h