As a Result of the Way Nerve Impulses Are Propagated,they

As a result of the way nerve impulses are propagated,they are unidirectional.Which of the following does not contribute to this phenomenon?

A) The time interval encompassed by the refractory period does not allow the impulse to travel in reverse.
B) Presynaptic neurotransmitters and postsynaptic receptors are separated.
C) Unidirectional sodium and potassium channels open only toward the axon of the nerve cell.
D) Sensory processes are oriented in such a manner that the information is targeted to the dendrites of the nerve cell.
E) none of the above