Two long conductors, separated by a distance $d$ carry current $I_1$ and $I_2$ in the same direction. They exert a force $F$ on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to $3d$. The new value of the force between them is

Question

( A ) $-2F$
( B ) $-2F/3$
( C ) $F/3$
( D ) $-F/3$