(85 POINTS!) A nerve signal is like a wave. How does this work?

A: An electrical wave moves down the axon by electrons moving from the place the signal started to the place it ends up.
B: A wave of reversal of the negative electrical potential inside the cell passes along the axon with ions moving in and out of the axon.
C: A wave of movement passes down the axon, in which the whole axon moves sideways in one place and then the next.
D: The density of the cytoplasm inside the axon changes from one place to the next as the signal moves along the axon.