The adjoining figure shows a conductor carrying a current $i$. The magnetic field at the origin is

• A
  $ - \frac{{\mu _0 i}}{{4r}}\,\left( {\frac{{\hat i}}{\pi } + \frac{{\hat j}}{2}} \right)$
• B
  $\frac{{\mu _0 i}}{{4r}}\,\left( {\frac{{\hat i}}{\pi } - \frac{{\hat j}}{2}} \right)$
• C
  $\frac{{\mu _0 i}}{{4r}}\,\left( {\frac{{\hat i}}{2} - \frac{{\hat j}}{\pi }} \right)$
• D
  $\frac{{\mu _0 i}}{{4r}}\,\left( {\frac{{2\hat i}}{\pi } + \hat j} \right)$