If `x^m` occurs in the expansion `(x+1//x^2)^n` , then the coefficient of `x^m` is `((2n)!)/((m)!(2n-m)!)` b. `((2n)!3!3!)/((2n-m)!)` c. `((2n)!)/(((2n-m)/3)!((4n+m)/3)!)` d. none of these