A current i ampere flows along the inner conductor of a coaxial cable and returns along the outer conductor of 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

  $\frac{{\mu }_0}{4\pi }\frac{2i}{r}$

• D

  $\frac{{\mu }_0}{4\pi }\frac{2\pi i}{r}$