A. According to the meaning of the question and chart analysis, A is a receptor, B is an afferent nerve, D is an efferent nerve, E is an effector, and A is wrong;

B, when unstimulated, the potential at the nerve fiber D is resting potential, and the potential distribution is positive potential outside the membrane, and negative potential inside the membrane, that is, positive outside and negative inside, B is wrong;

C, there are five synapses in the picture. When the hand is stabbed by a sharp weapon and retracts, the reflex arc is A→B→C→D→E, and C is correct;

D, neurotransmitters can be generally divided into excitatory and inhibitory two categories. Therefore, the transmitter released at the end of efferent nerve fiber from A may cause B's excitement or B's inhibition, and D is wrong.

So choose: C.