Determine Which of the Rational Functions Given Below Has the Following

Multiple Choice

Determine which of the rational functions given below has the following feature(s) .
-The $x$ -axis is its horizontal asymptote

A) $f ( x ) = \frac { 9 } { x - 4 }$
B) $f ( x ) = \frac { x + 4 } { x + 9 }$
C) $f ( x ) = \frac { 4 x - 1 } { x + 9 }$
D) $f ( x ) = \frac { x - 4 } { x }$