题目内容：
第49题___________
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 t.he brain.
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答案解析：