Two identical conducting wires $AOB$ and $COD$ are placed at right angles to each other. The wire $AOB$ carries an electric current $I_1$ and $COD$ carries a current $I_2$. The magnetic field on a point lying at a distance $d$ from $O$, in a direction perpendicular to the plane of the wires, will be given by:

1. A
   $\frac{{\mu }_0}{2\pi d}(I_1+I_2)$
2. B
   $\frac{{\mu }_0}{2\pi d}\sqrt{I_1^2+I_2^2}$
3. C
   $\frac{{\mu }_0}{2\pi d}(I_1-I_2)$
4. D
   $\frac{{\mu }_0}{2\pi d}\frac{I_1{I}_2}{I_1+I_2}$