To Measure the Voltage Across the Cell Membrane, You Would

To measure the voltage across the cell membrane, you would normally:

A) insert two electrodes into the axon and measure the voltage difference.
B) place one electrode on the outer surface of an axon's membrane and another inside the axon and measure the voltage difference.
C) place two electrodes on the outer surface of the axon's membrane and measure the voltage difference.
D) All of the answers are correct.