题目内容：
A And others have painful attacks all the time.
B These signals travel from nerve cells in the injured area, up the spinal cord (脊髓) to the brain, and back down again.
C It tells us that we are injured and should do something about it.
D They knew little about the process of pain itself.
E The other message moves at a speed of only one meter a second.
F And they send the second, slower message of pain to the brain.
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