The magnetic field at the origin due to a current element $i d l$ placed at a point with vector position $r$ is

• A
  $\frac{\mu_{0} i}{4 \pi} \frac{d l \times r}{r^{3}}$
• B
  $\frac{\mu_{0} i}{4 \pi} \frac{r \times d l}{r^{3}}$
• C
  $\frac{\mu_{0} i}{4 \pi} \frac{d l \times r}{r^{2}}$
• D
  $\frac{\mu_{0} i}{4 \pi} \frac{r \times d l}{r^{2}}$