Answer
Choice A
Work Step by Step
$\bf{\text{Solution Outline:}}$
A linear function is one where the exponent of all variables is $1.$ The only exception are linear equations of the form $x=a,$ where $a$ is a constant.
$\bf{\text{Solution Details:}}$
Among the choices, only $\text{
Choice A
}$ is an equation whose variables all have an exponent of $1$. Hence, it is a linear function.
