Magnetic field lines: special properties

They are open curves that begin at $\text{N}$‍ and end at $\text{S}$‍.

They are lines that emerge from the poles and go to infinity.

They are closed curves that go from $\text{N}$‍ to $\text{S}$‍ outside and $\text{S}$‍ to $\text{N}$‍ inside a magnet

They are closed curves in the shape of circles.