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.   \[\frac{{{\mu }_{0}}}{4\pi }\frac{2\pi \,i}{r}\]