Essential difference between electrostatic shielding by a conducting shell and magnetostatic shielding is due to ______. a. electrostatic field lines can end on charges and conductors have free charges. b. lines of B can also end but conductors cannot end them. c. lines of B cannot end on any material and perfect shielding is not possible. d. shells of high permeability materials can be used to divert lines of B from the interior region.