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根据下面内容，回答题：If we had to rely on only five senses for survival, we would be in very sad shape indeed. Wewouldn't know up from down. We wouldn't know when to eat or drink. We wouldn't know what ourmuscles were doing or what position our limbs were in. We wouldn't know when our body was dam-aged because we wouldn't feel pain. We might freeze to death without even a shiver, or overheat with-out a drop of sweat. The five senses--touch, taste, smell, hearing and sight--respond only to stimula-tion from the outside world, but the inside world of our bodies must also receive and respond to im-portant messages.
Our internal senses keep us alive and enable us to use our external senses. In effect, the internalsenses tell our brains how to run our bodies. Hunger or thirst registers in a part of the brain called thehypothalamus(丘脑下部) ,when a lack of food chemicals are detected in the blood.
Another internal sense that controls our balance is maintained by three fluid-filled loops in theinner ear. Changes in position and gravity affect the motion of this liquid and cause changes in thebrain. A sense called kinesthesia(肌肉运动知觉)lets us know the relative positions of parts of ourbodies. Even our breathing is caused by a sense that identifies an overabundance of carbon dioxideand a lack of oxygen in the blood.
No one has been able to count the number of internal senses. The presence of delicate internal senses shows just how marvelously complex we human beings are.
This passage deal mostly with the __________. A．internal senses
B．sense of balance
C．five senses
D．brain's function
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