Four thin straight long wires are all parallel to Z axis. They pass through the points A (3, 0, 0), B (0, 3, 0), C (-3, 0, 0) and D (0, -3, 0). They all carry currents in ̂ direction of magnitudes 0.3 A, 0.6 A, 0.3 A and 0.3 A respectively. The magnitude of magnetic field at the origin O due to
(a) wires at A and C is zero
(b) wires at A and B is 2√2 x 10-8 T
(c) wires at A and D is 2√2 x 10-8 T
(d) all wires is 2 x 10-8 T
