The absolute refractory period of an action potential

A) only ensures one-way travel down an axon.
B) only allows a neuron to ignore a second signal sent that closely follows the first.
C) only prevents summation of action potentials.
D) ensures one-way travel down an axon and allows a neuron to ignore a second signal sent that closely follows the first.
E) ensures one-way travel down an axon, allows a neuron to ignore a second signal sent that closely follows the first, and prevents summation of action potentials.