Specify the Domain for the Function $f ( x ) = \sqrt { x ^ { 2 } + 7 x - 18 }$

Multiple Choice

Specify the domain for the function. $f ( x ) = \sqrt { x ^ { 2 } + 7 x - 18 }$

A) $D = ( - \infty , - 9 ] \cup [ 2 , \infty )$
B) $D = ( - \infty , - 2 ) \cup ( 9 , \infty )$
C) $D = [ - 9,2 ]$
D) $D = [ 2 , \infty )$