A long straight cylindrical shell has an inner radius R_i and an outer radius R_0. It carries a current i, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollow region (r < R_i).The magnetic field is zero everywhere outside the shell (r > R_0). We conclude that the wire:

a. is on the cylinder axis and carries current i in the same direction as the current in the shell
b. may be anywhere in the hollow region but must be carrying current i in the direction opposite to that of the current in the shell
c. may be anywhere in the hollow region but must be carrying current i in the same direction as the current in the shell
d. is on the cylinder axis and carries current i in the direction opposite to that of the current in the shell
e. does not carry any current