题目内容：
根据以下材料回答第 1～4 题：If we had to rely on only five senses for survival，we would be in very sad shape indeed．We wouldn’t know up from down．We wouldn’t know when to eat or drink．We wouldn’t know what our muscles were doing or what position our limbs were in．Wewouldn’t know when our body was damaged because we wouldn’t feel pain．We mightfreeze to death without even a shiver，or overheat without a drop of sweat．The five sen-ses--touch，taste，smell，hearing and sight-respund only to stimulation from the outside world，but the inside world of our bodies must also receive and respond to important messages．
Our internal senses keep us alive and enable us to use our external senses．In effect，the intemal senses tell our brains how to run our bodies．Hunger or thirst register in a part of the b商n called the hypothahmus(丘脑下部)，when a lack of food chemicals are detmted in the blood．
Another internai sense that controls our balance is maintained by three fluid-filled loops in the inner ear．Changes in position and gravity affect the motion of this liquid and cause changes in the brain．A sense called kinesthesia(肌肉运动知觉)lets us know the relative positions of parts of our bodies．Even our breathing is caused by a sense that in—dentfies an overabundance of carbon dioxide and lack of oxygen in the blood．
No one has been able to count the unmber of internal senses．The presence of delicate internal senses shows just how marvelously complex we human beings are．
This passage deal mostly with the．
参考答案：
答案解析：