Answer
We can rank the three sections according to the radius:
$C \gt B \gt A$
Work Step by Step
The current $i$ flowing in the wire is constant throughout the wire.
We can write an expression for the current:
$i = ne~v_d~A$
$ne$ is the carrier charge density which is an intrinsic property of copper
$v_d$ is the drift speed
$A$ is the cross-sectional area of the wire
We can write an expression for the cross-sectional area:
$A = \frac{i}{ne~v_d}$
From this expression, we can see that if the drift speed $v_d$ has a larger value,
the area must have a smaller value, and in turn, the radius must have a smaller value.
We can rank the three sections according to the radius:
$C \gt B \gt A$
