The correct answer is "they form straight lines."
The statement about magnetic field lines that is true is "they form straight lines."
If we observe a magnet we can realize that magnetic field lines point toward the south pole of a magnet and away from the north pole.
As we have studied the laws of magnetism in previous lessons, unlike poles attract and like poles repel.
We have to say that magnetic lines are continuous and they never intersect.
The force exerted by magnets is called magnetism. The motion of the electric changes in magnets is what produces this magnetism.