Which one of the following does not act as a neurotransmitter ?

Neurotransmitters are chemicals released from the synaptic vesicles at the axon terminal; they carry the nerve impulse across a chemical synapse.
Acetylcholine is the neurotransmitter at neuromuscular junctions and at cholinergic synapses.
Norepinephrine (noradrenaline) is the neurotransmitter of the adrenergic (sympathetic) nerve fibres.
Epinephrine (adrenaline) also acts as a neurotransmitter in some parts of the nervous system, besides being a hormone of the adrenal medulla.
Cortisone is a steroid hormone (a glucocorticoid) of the adrenal cortex; it acts on metabolism through the blood and is not released at synapses.
So the one that does not act as a neurotransmitter is cortisone.