A small coil of `N` turns has an effective area `A` and carries a current `I`. It is suspended in a horizontal magnetic field `vecB` such that its plane is perpendicular to `vecB`. The work done in rotating it by `180^(@)` about the vertical axis is
A. `NAIB`
B. `2NAIB`
C. `2piNAIB`
D. `4piNAIB`