Electro-magnets are created
a) applying a charge to a magnetic material, wrapped in an insulator, which creates an electro magnetic field around the magnet.
b) covering a magnet with insulation in applying an alternating electrical current to the magnet.
c) twisting a ferromagnetic material, wrapping in an insulator, and applying a direct current to the coil.
d) wrapping in insulated wire around a medal with ferromagnetic properties and applying an electric current.