If in a circular coil $A$ of radius $R$, current $i$ is flowing and in another coil $B$ of radius $2R$ a current $2i$ is flowing, then the ratio of the magnetic fields, $B_A$ and $B_B$ produced by them will be :

Question

( A ) $2$
( B ) $1/2$
( C ) $4$
( D ) $1$