A uniform conducting rectangular loop of sides l, b and mass m carrying current i is hanging horizontally with the help of two vertical strings. There exists a uniform horizontal magnetic field B which is parallel to the longer side of loop. The value of tension which is least is
A. `(mg-Bb)/2`
B. `(mg+Bb)/2`
C. `(mg-2iBb)/2`
D. `(mg+2Bb)/2`