The Lines of a magnetic field do not cross; why? NABTEB QUESTION

The lines of force of a magnetic field do not cross because the line of force is the line along which a free N pole would tend to move if placed in the field or it is a line such that a tangent to it at any point gives the direction of the field at that point. Therefore if they cross, it means a free N pole will have two directions it can go at the point of crossing but this is not observed.