Five events in the transmission of a nerve impulse across a synapse are given below:
$a.$ Certain ion channels open,allowing ions to enter and generate a new action potential in the post-synaptic neuron.
$b.$ Neurotransmitter molecules bind to receptors on the post-synaptic membrane.
$c.$ Synaptic vesicles fuse with the pre-synaptic membrane,and the neurotransmitter is released into the synaptic cleft. Depolarization of the pre-synaptic membrane is induced.
$d.$ An action potential reaches the axon terminal.
What is the correct sequence of these events?

• A
  $d \rightarrow c \rightarrow b \rightarrow a$
• B
  $a \rightarrow b \rightarrow c \rightarrow d$
• C
  $a \rightarrow b \rightarrow d \rightarrow c$
• D
  $d \rightarrow c \rightarrow a \rightarrow b$