A Wire Solenoid with 100 Total Turns Is Bent into the Shape

Multiple Choice

A wire solenoid with 100 total turns is bent into the shape of a torus (doughnut) having a radius $r = 5$ cm. A 730-mA current passes through the wire. The magnetic field inside the torus is

A) 5.6 mT.
B) 13 mT.
C) 0.29 mT.
D) 23 mT.