<h2><u>Answer:</u></h2>
Neurotransmitter is the correct answer.
<h3><u>Explanation:</u></h3>
The neurotransmitter, additionally called chemical transmitter or compound flag-bearer, any of a gathering of synthetic operators discharged by neurons (nerve cells) to animate neighboring neurons or muscle or organ cells, in this manner enabling driving forces to be passed starting with one cell then onto the next all through the sensory system.
A is an example of direct characterization
