求指导本题解题过程，谢谢您！21、甲四-|||-以下展开式错误的是 () .-|||-A dfrac (1)({(1-x))^2}=sum _(n=1)^infty n(x)^n-1 |x|lt 1-|||-B ^(x^3)=sum _(n=0)^infty dfrac ({x)^3n}((3n)!)! |x|lt +infty -|||-C ln 2=1-dfrac (1)(2)+dfrac (1)(3)-dfrac (1)(4)+... -|||-D dfrac (1)(1+{x)^2}=sum _(n=0)^infty ((-1))^n(x)^2n |x|lt 1

求指导本题解题过程，谢谢您！