Answer:
The correct answer is option B ( ligand gated channels opened by neurotransmitter molecules).
Explanation:
Input region or postsynaptic region or dendrite is the site of neuron cell which receives the impulse from the pre-synaptic neuron at the synaptic junction.
The cell membrane of the dendrite is embedded with ligand-gated channels which opens up in response to the ligand (neurotransmitters) produced by the neurotransmitter vesicle of axon or output region of neuron.
The neuromuscular junction is such a case where acetylcholine receptors present in the dendrite opens in the presence of acetylcholine.
Thus, option B ( ligand-gated channels opened by neurotransmitter molecules) is the correct option.