Magnetic Field of Straight Wires question from JEE Main 2010 (AIEEE)

Answer: (a)

1. For a current out of the page, the field on $XX'$ points up to the right of the wire and down to its left, with $B \propto \frac{1}{r}$.
2. Left of both wires: both fields down, $B < 0$. Right of both: both up, $B > 0$.
3. Between: large positive near the left wire, zero at the midpoint, large negative near the right wire.
4. So the answer is (a).