What causes the release of acetylcholine (ach) into the synaptic cleft of a cholinergic

what causes the release of acetylcholine (ach) into the synaptic cleft of a cholinergic synapse? answer unselected the binding of acetylcholine to postsynaptic receptors unselected the hyperpolarization of the synaptic terminal unselected the enzyme acetylcholinesterase unselected calcium ions entering the cytoplasm of the synaptic terminal