Answer
We can rank the sections of the wire according to the magnitude of the current density:
$B \gt C \gt A$
Work Step by Step
When a current flows through a wire, the current that flows through any cross-section of the wire is constant.
We can write a general expression for the current density:
$J = \frac{i}{A}$
From this equation, we can see that the current density is greater when the cross-sectional area is smaller.
We can rank the sections of the wire according to the magnitude of the current density:
$B \gt C \gt A$
