Why Are Action Potentials Usually Conducted in One Direction

Why are action potentials usually conducted in one direction?

A) The axon hillock has a higher membrane potential than the terminals of the axon.
B) Voltage- gated channels for both Na+ and K+ open in only one direction.
C) The brief refractory period prevents reopening of voltage- gated Na+ channels.
D) Ions can flow along the axon in only one direction.
E) The nodes of Ranvier conduct potentials in one direction.