All of US have felt pain.We have cut ourselves.We have been burned.Or we have had headaches.Some of us suffer pain rarely pain rarely. (46)
Pain can take complete control of our body and mind，making it impossible to move and even to think.Yet we need pain.Without it，we would not know.1f we have hurt ourselves.It is our body’s warning system. (47)
Pain is the most common reason we go to a doctor It is the most common reason we take medicines.Until recently，however, most doctors knew of only a few drugs that stopped some pains (48)But new knowledge about the process of pain is helping them to control pain better.
Scientists have learned that the sense of pain is made up of both chemical and electrical signals. (49)Scientists also have learned that the nervous system sends two different kinds of pain messages to the brain：one very fast，the other slow.The first message is the warning signal.It moves at a speed of 30 meters a second.In less than a second，the brain understands that part of the body is hurt and how badly it is injured. (50)It tells us not to use the injured part until it heals.
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 013~meter a second.
F And they send the second，slower message of pain to the brain.
答案解析
46 A 文章第一段提到，我们都曾感觉过疼痛。从空格前一句的内容，即“有些人很少遭受疼痛之苦”，可以推断空格处句子的内容应当与这一句的内容相反，即“另外一些人却总是遭受疼痛的袭击”。
47 C 空格前的句子讲到，疼痛是我们身体的警报系统。因此接下来的句子应该说明这样说的原因。
48 D 空格后一句讲到，然而，有关疼痛过程的新知识使医生得以更好地控制疼痛。由此可见，空格处句子的内容应与此句内容相反，即医生对疼痛过程了解得很少。
49 B 空格前一句中的“chemical and electrical signals”等词语是对空格处句子的很好提示。
50 E 文章第四段最后一句提到了“two different kinds of pain messages”，而文章最后一段第一句中又用了“The first message”，显然，空格处的句子应以“The other message”开始。