$8$

$13.$ For $z=x^2-x{y}^2$ with $x=2s-t+u$ and $y=s{t}^2{u}^2$ find the partial derivatives $\frac{\text{d}\text{e}\text{l}\text{z}}{\text{d}\text{e}\text{l}\text{s}},\frac{\text{d}\text{e}\text{l}\text{z}}{\text{d}\text{e}\text{l}\text{t}}$ and $\frac{\text{d}\text{e}\text{l}\text{z}}{\text{d}\text{e}\text{l}\text{u}}$ at the point $(s,t,u)=(2,1,-1).$

A$.0$

B$.(0,-8)$

C$.(1,4,-4)$

D$.2x-2xy$

E$.(2,-1,1)$

F$.(-8,-32,32)$

G$.(2s-t+u{)}^2-(2s-t+u)(s{t}^2{u}^2{)}^2$

$H.$ none of the above