搜题请搜索小程序“爱下问搜题”
问题 选择题

胸廓的变化与呼吸的关系（　　）

A．胸廓扩大导致吸气

B．吸气导致胸廓扩大

C．胸廓扩大与吸气没有关系

D．以上都不是

答案

呼吸运动是由呼吸肌的收缩和舒张引起的，包括吸气和呼气两个过程：吸气时，膈肌与肋间肌收缩，引起胸腔前后、左右及上下径均增大，胸廓扩大，肺随之扩大，造成肺内气压小于外界大气压，外界气体进入肺内，形成主动的吸气运动；呼气时，膈肌和肋间外肌舒张时，肋骨与胸骨因本身重力及弹性而回位，结果胸廓缩小，肺也随之回缩，造成肺内气压大于外界气压，肺内气体排出肺，形成被动的呼气运动．因此，胸廓扩大导致吸气，胸廓缩小导致呼气．

故选：A．

单项选择题

In 1575--over 400 years ago the French scholar Louis Le Roy published a learned book in which he voiced despair over the changes caused by the social and technological innovations of his time, what we now call the Renaissance. We, also, feel that our times are out of joint; we even have reason to believe that our descendants will be worse off than we are.
The earth will soon be overcrowded and its resources exhausted. Pollution will ruin the environment, upset the climate and endanger human health. The gap in living standards between the rich and the poor will widen and lead the angry, hungry people of the world to acts of desperation including the use of nuclear weapons as blackmail. Such are the inevitable consequences of population and technological growth if present trends continue.
The future is never a projection of the past. Animals probably have no chance to escape from the tyranny of biological evolution, but human beings are blessed with the freedom of social evolution. For us, trend is not destiny (fate). The escape from existing trends is now facilitated by the fact that societies anticipate future dangers and take preventive steps against expected changes.
Despite the widespread belief that the world has become too complex for comprehension by the human brain; modern societies have often responded effectively to critical situations. The decrease in birth rates, the partial prohibition of pesticides and the rethinking of technologies for the production and use of energy are but a few examples illustrating a sudden reversal of trends caused not by political upsets or scientific breakthroughs, but by public awareness of consequences.
Even more striking are the situations in which social attitudes concerning future difficulties undergo rapid changes before the problems have come to pass--witness the heated arguments about the problems of behavior control and of genetic engineering even though there is as yet no proof that effective methods can be developed to manipulate behavior and genes on a population scale.
One of the characteristics of our times is thus the rapidity with which steps can be taken to change the orientation of certain trends and even to reverse them. Such changes usually emerge from grass root movements rather than from official directives.
Notes: Renaissance (14--15 世纪欧洲)文艺复兴(时期)。tyranny 暴虐统治；暴虐行为。are blessed with幸有；有幸得到。but a few 只是几个。come to pass 发生，实现。as yet 至今。grass root 群众。

The best illustration of the meaning of "trend is not destiny" in Para. 3 is that

A．human beings are blessed with the freedom of social evolution.

B．the world has become too complex for human beings to modify.

C．preventive steps against catastrophes are difficult to be adopted.

D．the earth will soon be overcrowded and its resources exhausted.
查看答案
单项选择题

位错的具有重要的性质，下列说法不正确的是（）。

A.位错不一定是直线

B.位错是已滑移区和未滑移区的边界

C.位错可以中断于晶体内部

D.位错不能中断于晶体内部
查看答案