Draw the patterns of magnetic field lines due to a bar magnet. The magnetic field lines are closed curves. Why?

(N/A) Outside the magnet,the magnetic field lines emerge from the north pole and merge into the south pole.
Inside the magnet,the direction of the field lines is from the south pole to the north pole.
Because the field lines are continuous and form a complete path from the north pole to the south pole outside and from the south pole to the north pole inside,they form closed curves.