Why are action potentials usually conducted in one direction?

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