A current `i` ampere flows along the inner conductor of a coaxial cable and returns along the outer conductor fo the cable, then the magnetic induction at any point outside the conductor at a distance `r` metre from the axis is
A. `infty`
B. zero
C. `(mu_(0))/(4pi)(2i)/(r)`
D. `(mu_(0))/(2pi)(2pii)/(r)`
