Using the information in the text, complete each sentence 14-18 with an expression from the list below.
For each sentence(14-18), mark one letter(A~G)on your Answer Sheet.
Do not mark any letter twice.
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 1of it.

填空题 Some pain is the result of 1.

填空题 People suffer both physically and emotionally if they have 1.

填空题 It is found that men have fewer 1than women.

填空题 Study on animals may finally discover some new 1for human beings.