Find Values Of $x$ And $y$ Such That Both $f_{x}(x, y)=0$ And $f_{y}(x, y)=0$

Multiple Choice

Find values of $x$ and $y$ such that both $f_{x}(x, y) =0$ and $f_{y}(x, y) =0$ .
- $f(x, y) =3 x^{2}+3 y^{2}-6 x-6 y+2$

A) $x=0, y=0$
B) $x=6, y=6$
C) $x=3, y=3$
D) $x=1, y=1$