[A] : The synaptic knob contains mitochondria and synaptic vesicles rich in chemical trans- mitters.
[R]: Chemical transmitters are neurohor- mones. Their release is related to `Ca^(++)` in- flux.
A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false