Rewrite the Quadratic Function in Standard Form by Completing the Square

Multiple Choice

Rewrite the quadratic function in standard form by completing the square.
- $$f ( x ) = x ^ { 2 } - 18 x$$

A) $f ( x ) = ( x + 18 ) ^ { 2 } - 18$
B) $f ( x ) = ( x - 18 ) ^ { 2 } - 324$
C) $f ( x ) = ( x + 9 ) ^ { 2 } - 9$
D) $f ( x ) = ( x - 9 ) ^ { 2 } - 81$