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问题 选择题

人体呼出气体能使澄清石灰水很快变浑浊，而空气却不能，证明人体呼出的气体（　　）

A．含有氧气

B．含有二氧化碳

C．含有较多氧气

D．含有较多二氧化碳

答案

解；呼吸作用是生活细胞中有机物在氧的作用下被分解成二氧化和水，并释放出能量的过程．二氧化碳能使澄清的石灰水变浑浊是二氧化碳的特性．所以向澄清的石灰水内吹气，石灰水会变得浑浊，这说明人体呼出的气体中含有较多的二氧化碳．

故选：D

单项选择题

Passage One


There are two types of people in the world. Ahhough they have equal degree of health and wealth and other comforts of life, one becomes happy and the other becomes unhappy. This arises from the different ways in which they consider things ,persons, events and the resulting effects upon their minds.
People who are to be happy fix their attention on the convenience of things:the pleasant parts of conversation, the well prepared dishes, the goodness of the wine and the fine weather. They enjoy all the cheerful things. Those who are to be unhappy think and speak only of the opposite things. Therefore, they are continually dissatisfied. By their remarks, they sour the pleasure of society, offend (hurt) many people, and make themselves disagreeable everywhere. If this turn of mind was founded in nature, such unhappy persons would be the more to be pitied. The intention of criticizing and being disliked is perhaps taken up by imitation. It grows into a habit, unknown to its possessors. The habit may be p, but it may be cured when those who have it realize its bad effects on their interests and tastes. I hope this little warning may be of service to them, and help them change this habit.
Although in fact it is chiefly an act of the imagination, it has serious results in life since it brings on deep sorrow and bad luck. Those people offend many others;nobody loves them, and no one treats them with more than the most common politeness and respect. This frequently puts them in bad temper and draws them into arguments. If they aim at getting some advantages in social position or fortune, nobody wishes them success. Nor will anyone start a step or speak a word to favor their hopes. If they bring on themselves public objections, no one will defend or excuse them, and many will join to criticize their wrong doings. These should change this bad habit and be pleased with what is pleasing, without worrying needlessly about themselves and others. If they do not, it will be good for others to avoid any contact with them. Otherwise, it can be disagreeable and sometimes very inconvenient, especially when one becomes mixed up in their quarrels.

In this passage, the writer mainly______.

A．describes two types of people

B．laughs at the unhappy people

C．suggests the unhappy people should get rid of the habits of unhappiness

D．tells people how to be happy in life
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单项选择题

生产者购买行为类型中，最简单的是（）。

A.直接续购

B.修正重购

C.新购

D.委托采购
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