Rút gọn các phân thức :
\(A=\dfrac{x^2\left(y-z\right)+y^2\left(z-x\right)+z^2\left(x-y\right)}{xy^2-xz^2-y^3+yz^2}\)
\(B=\dfrac{a^3-b^3+c^3+3abc}{\left(a+b\right)^2+\left(b-c\right)^2+\left(c+a\right)^2}\)
\(C=\dfrac{a^3b-ab^3+b^3c-bc^3+c^3a-ca^3}{a^2b-ab^2+b^2c-bc^2+c^2a-ca^2}\)