What does "a" and "b" indicate in the given diagram ?
(A) a = Synaptic bulb b = Phagocgtosis
(B) a = Presynaptic b = Phagocytosis
(C) a = Synaptic gap b = Secretion of neurotranmetter
(D) a = Presynaptic bulb b = Secretion neurotranmitter
