A long straight wire of circular cross section of radius ҅ a carries a steady current I.The current

A long straight wire of circular cross section of radius ҅a᾿ carries a steady current I. The current is uniformly distributed across its cross section. The ratio of magnitudes of the magnetic field at a point a/2 above the surface of wire to that of a point a/2 below its surface is
(A) 4:1 (B) 1:1 (C) 4: 3 (D) 3 :4