Which of the following is a valid exclusion for the algebraic fraction 8ab^2x/4a^2b - 8ab^2
A. a=/ 0, b =/ 0, a = / b
B. a = / 0, b =/ 0
C. a =/ 0, b =/ 0, a = / 2b
D. b = / 0, a = / b