Which of the Following Statements Regarding the Perception of Pain

Which of the following statements regarding the perception of pain is true?

A) Substance P is an important neurotransmitter in specific pain pathways
B) Transmission of information in the pain pathway may be inhibited by activation of neurons that synthesize endorphins
C) Synaptic activity in afferent neurons associated with pain receptors can be inhibited by axon-axon synapses with neurons from descending pathways
D) Both substance P is an important neurotransmitter in specific pain pathways and transmission of information in the pain pathway may be inhibited by activation of neurons that synthesize endorphins are true
E) All of the choices are true