Two very long,straight and insulated wires are kept at a $90^o$ angle from each other in the $xy$-plane as shown in the figure. These wires carry a current of equal magnitude $I$,whose directions are shown in the figure. The net magnetic field at point $P$ will be:

• A
  $\frac{{{\mu _0}I}}{{2\pi d}}\left( {\hat x + \hat y} \right)$
• B
  $\frac{{ + {\mu _0}I}}{{\pi d}}\left( {\hat z} \right)$
• C
  Zero
• D
  $-\frac{{{\mu _0}I}}{{2\pi d}}\left( {\hat x + \hat y} \right)$