For the Given Pair of Functions, Find the Requested Function $f(x)=x^{2}-x-6$

Multiple Choice

For the given pair of functions, find the requested function.
-If $f(x) =x^{2}-x-6$ and $g(x) =x-1$ , find $(f g) (x)$ .

A) $x^{3}-2 x^{2}-6 x+6$
B) $x^{3}-2 x^{2}-7 x-6$
C) $x^{3}-5 x+6$
D) $x^{3}-2 x^{2}-5 x+6$