question_answer 31)

    S is the surface of a lump of magnetic material. Lines of  are necessarily continuous across S Some lines of  must be discontinuous across S Lines of are necessarily continuous across S Lines of  cannot all be continuous across S

Answer:

   (a,d)The lines of magnetic field induction  are necessarily continuous across the surface S of a lump of magnetic material. Outside the lump of magnetic material,  and inside the lump of magnetic material, whereis the relative permeability of material. Thus the lines of H cannot all be continuous across surface S.