Magnetic Field of Straight Wires question from NEET 1996 (AIPMT)

Answer: (b)

1. Take one current along $+y$ and the other along $+x$. At a point $(x, y)$ in the plane, the first gives $B \propto \frac{1}{x}$ into the page, the second gives $B \propto \frac{1}{y}$ out of the page.
2. They cancel when $x = y$ (both positive or both negative), i.e. on the line $y = x$.
3. That line is $AB$ (first and third quadrants); on $CD$ the two fields add.
4. So the answer is (b) on $AB$.