An Action Potential Has Reached the Synaptic End Bulb, but There

Multiple Choice

An action potential has reached the synaptic end bulb, but there is no neurotransmitter release. This could be caused by

A) failure of the voltage-gated k⁺ channels to open, thus preventing repolarization
B) failure of the synaptotagmin to form channels for the neurotransmitter to cross the membrane
C) failure of voltage-gated ca²⁺ channels to open, preventing ca²⁺ from entering the cell
D) failure of kinesins to transport vesicles across the synaptic cleft