Two thin, long parallel wires separated by a distance ‘$d$ ’ carry a current of ‘$i$ ’ A in the same direction. They will:

1. A
   attract each other with a force of ${\mu }_0{i}^2/(2\pi d)$
2. B
   repel each other with a force of ${\mu }_0{i}^2/(2\pi d)$
3. C
   attract each other with a force of ${\mu }_0{i}^2/(2\pi d^2)$
4. D
   repel each other with a force of ${\mu }_0{i}^2/(2\pi d^2)$