You have learned that dissolved materials always diffuse from where there is more of them to where there is less. Oxygen from the air dissolves in the moisture on the lining of the air sac and diffuses through the lining into the blood. Meanwhile, carbon dioxide diffuses from the blood into the air sac. The blood then flows from the lungs back to the heart, which sends it out to all other parts of the body.
Soon after air goes into an air sac, it gives up some of its oxygen and takes in some carbon dioxide from the blood. To keep diffusion going as it should, this carbon dioxide must be gotten rid of. Breathing, which is caused by movements of the chest, forces the used air out of the air sacs in your lungs and brings in fresh air. The breathing muscles are controlled automatically so that you breathe at the proper rate to keep your air sacs supplied with fresh air.
Ordinarily, you breathe about twenty-two times a minute. Of course, you breathe faster when you are exercising and slower when you are resting. Fresh air is brought into your lungs when you breathe in, or inhale, while used air is forced out of your lungs when you breathe out, or exhale.
26. In the respiratory process, only one of the following actions takes place: it is_______.
A. the diffusion of blood through capillary walls into air sacs
B. the diffusion of carbon dioxide through capillary and air sac walls into the blood
C. the diffusion of oxygen through the air sac and capillary walls into the blood
D. the exchange of nitrogen within air sacs
27. The number of times per minute that you breathe is_______.
A. independent of your rate of exercise
B. fixed at twenty-two times per minute
C. influenced by your age and sex
D. controlled automatically by an unspecified body mechanism
28. The process by which carbon dioxide and oxygen are transferred does not depend on
A. the presence of nitrogen in the blood
B. breathing muscles
C. the flow of blood
D. the moisture in the air sac linings
29. The authors style in this passage can best be described as---------.
A informal and matter of fact B. impersonal
C. personal P- matter of fact and formal
30. Which of the following words can replace the word exhale? A. Breathe out. B. Breathe in.
C. Diffuse. D. Exchange.
26. C 27. D 28. A 29. A 30. A
英语四级复合式听写原文(昂立版)
英语四级短对话解析(昂立)
四级考前30天听力必背词汇短语集锦
12月的四级听力真题点评(恩波版)
四级的听力对话答题小技巧
英语周报四级听力模拟试题(三)
2014年英语四级考试听力必背场景词汇
四级听力笔记短对话的补充场景
英语周报四级听力模拟试题(七)
应付大学英语四级写作中词汇匮乏的技巧
英语周报四级听力模拟试题(二)
四级听力关键正确接收有效信息
英语四级的必过两大支柱听力辅导
大学英语四级考试听力的葵花宝典
英语四级考试听力技巧多积累多练习
大学英语四级听力训练方案及例题练习的演示
四级听力重点主题与场景分析
四级听力考试必备的词组
英语四级复合式听写答案(恩波版)
大学英语四级的考试听力高分之路
四级的最后冲刺:听力完整训练
英语四级听力原文部分(昂立)
12月的英语四级听力真题答案(恩波版)
英语四级的备考听力课堂笔记(二)
英语四级听力原文
大学英语四级考试各类听力场景高频词汇
四级听力笔记原则思路及标志词
英语周报四级听力模拟试题(八)
名师分析英语四级听力重点主题短语词汇大全
12月的英语四级听力解析(昂立版)
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |