What is a difference between the magnetic fields of a regular bar magnet and an electromagnet?
a. a bar magnet's field is temporary, but an electromagnet's is permanent.
b. a bar magnet's field is permanent, but an electromagnet's is temporary.
c. a bar magnet is made of iron, but an electromagnet is made of plastic.
d. there is always an electric current flowing around an electromagnet.

B. a bar magnet's field is permanent, but an electromagnet's is temporary.
a bar magnet has a permanent magnetic field which has a constant strength and cannot be varied. on the other hand, an electromagnet is one in which magnetism is induced temporarily and strength of magnetic field can vary depending on a number of factors. when current passing through coils of wire in an electromagnet stops, the electromagnet also does not act as a magnet anymore