(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.