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Two straight horizontal parallel wires are carrying the same current in the same direction, d is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires

(a) At a distance d/2 from any of the wires

(b) At a distance d/2 from any of the wires in the horizontal plane

(c) Anywhere on the circumference of a vertical circle of radius d and centre halfway between the wires

(d) At points halfway between the wires in the horizontal plane