Which of the following is the range of the exponential function $f(x)=a^{x}, a>0$ and $a \neq 1 ?$
$$
\begin{array}{ll}{\text { (a) }(-\infty, \infty)} & {\text { (b) }(-\infty, 0)} \\ {\text { (c) }(0, \infty)} & {\text { (d) }(-\infty, 0) \cup(0, \infty)}\end{array}
$$