The Largest Set on Which the Function $f ( x ) = 5 ^ { - x }$

Multiple Choice

The largest set on which the function $f ( x ) = 5 ^ { - x }$ is decreasing is

A) $( - 2 , \infty )$
B) $( - \infty , 2 )$
C) $( 2 , e )$
D) $( e , \infty )$
E) $( 2 , e ) \cup ( e , \infty )$