Multiple Choice A function $f$ is [(a) increasing, (b) decreasing,
(c) nonincreasing, (d) nondecreasing, (e) constant] on an interval $I$ if, for any choice of $x_{1}$ and $x_{2}$ in $I,$ with $x_{1}<x_{2},$ then $f\left(x_{1}\right)<f\left(x_{2}\right)$.