What decribes the tendency for the conducting material to oppose the flow of electrons

Answer choices please? 

Which principle states: "geologic processes taking place on earth today operated similarly in the past and can be used to explain past geologic events"? a. lateral continuity

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.