When an Axon Is Severed, What Likely Causes the Presynaptic

When an axon is severed, what likely causes the presynaptic cell to withdraw axons?

A) The postsynaptic neuron dying, initiating apoptotic cascades
B) The postsynaptic neuron condensing, and widening the synapse to pull axons away
C) Invading macrophages crowding into the synapse, effectively pushing the presynaptic neuron away
D) The de-differentiation of Schwann cells pulling the postsynaptic neuron away
E) Both the pre- and postsynaptic neurons expressing repulsive cues, such as Slit and its Robo receptor