This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Why is neuronal synaptic conduction mostly ohodromic? 
Select and explain. 
A. Dendrites cannot be depolarized, B. Once repolarized, an area cannot be depolarized, C. The strength of antidromic impulse is less, D. Chemical mediator is localised only in the presynaptic terminal
D: Chemical mediator is localised only in the presynaptic terminal
Answer: D: Chemical mediator is localised only in the presynaptic terminal 
Explanation: Characteristic of chemical synapses is that it always transmit signals in one direction, from the neuron that secretes the transmitter substance, called the presynaptic neuron, to the neuron on which the transmitter acts, called the postsynaptic neuron. Ref: Principles of Animal Physiology By Moyes, Page 218.