Fill in the Blank with One of the Words or Phrases

Multiple Choice

Fill in the blank with one of the words or phrases listed below. Some words or phrases may be used more than once. $$\begin{array} { l l l l } \text { inverse } & \text { common } & \text { composition symmetric } & \text { exponential } \\\text { vertical } & \text { logarithmic } & \text { natural half-life } & \text { horizontal }\end{array}$$
-A function of the form $f ( x ) = b ^ { x }$ is called $a ( n )$ ـــــــــ function if $\mathrm { b } > 0$ , $\mathrm { b }$ is not 1 , and $\mathrm { x }$ is a real number.

A) logarithmic
B) symmetric
C) exponential
D) inverse