填空题 A. chronic pain
B. brain chemical
C. nerve receptors
D. a clear definition
E. damaged nerves
F. painkilling therapies
G. an emotional response

填空题 As scientists don't know much about pain, it's hard to provide ______ of it.

填空题 Some pain is the result of ______.

填空题 People suffer both physically and emotionally if they have ______.

填空题 It is found that men have fewer ______ than women.

填空题 Study on animals may finally discover some new ______ for human beings.