A current of $1/\left(4\pi \right)$ ampere is flowing in a long straight conductor. The line integral of magnetic induction around a closed path enclosing the current carrying conductor is

• A

  ${10}^{-7}$ weber per metre

• B

  $4\mathrm{\pi }\times {10}^{-7}$ weber per metre

• C

  $16\mathrm{\pi }\times {10}^{-7}$ weber per metre

• D

  zero