Which of the Following Manipulations Would Reduce the Release of Neurotransmitter

Multiple Choice

Which of the following manipulations would reduce the release of neurotransmitter from a presynaptic neuron terminal?

A) reduction in extracellular calcium ion concentration at the axon terminal
B) increase in extracellular sodium and potassium ion concentrations at the axon terminal
C) addition of tetrodotoxin to the extracellular fluid at the axon terminal
D) All of the above manipulations would reduce the release of neurotransmitter.