The correct answer is: D. neither a maximum nor minimum.
The function $f(x) = |x|$ is a piecewise function. It is defined as $f(x) = x$ for $x \ge 0$ and $f(x) = -x$ for $x < 0$.
At $x = 0$, the function changes its direction from increasing to decreasing. This is not a point of maximum or minimum, but a point of inflection.
A point of maximum or minimum is a point where the function changes its direction from increasing to decreasing or vice versa, and the function value is either the largest or smallest value in the neighborhood of the point.
A point of inflection is a point where the function changes its concavity from concave up to concave down or vice versa.
In the case of $f(x) = |x|$, the function changes its concavity at $x = 0$. However, the function value at $x = 0$ is not the largest or smallest value in the neighborhood of the point. Therefore, $x = 0$ is a point of inflection, but not a point of maximum or minimum.