A single-turn rectangular coil is rotated with constant angular speed in a uniform magnetic field. The induced emf in the coil becomes zero whenever:
a) the coil has rotated through 90∘ from the position of maximum flux
b) the plane of the coil is perpendicular to the magnetic field lines
c) the coil has rotated through 45∘ from the position of zero flux
d) the plane of the coil is parallel to the magnetic field lines