Find the Interval(s) Where the Function $f(x)=3^{-x}$ Is Decreasing $(0, \infty)$ B) $(-\infty, 0)$

Multiple Choice

Find the interval(s) where the function $f(x) =3^{-x}$ is decreasing.

A) $(0, \infty)$
B) $(-\infty, 0)$
C) $(-\infty, 0) \cup(0, \infty)$
D) $(-\infty, 3) \cup(3, \infty)$
E) $(-\infty, \infty)$