试题与答案

水的沉淀法处理的基本原理是什么？试分析球形颗粒的静水自由沉降（或上浮）的基本规律，影

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题型：问答题 简答题

题目：

水的沉淀法处理的基本原理是什么？试分析球形颗粒的静水自由沉降（或上浮）的基本规律，影响沉降或上浮的因素是什么？

答案：

参考答案：

基本原理：沉淀法是利用水中悬浮颗粒的可沉降性能，在重力作用下产生下沉作用，以达到固液分离的一种过程。

基本规律：静水中悬浮颗粒开始沉降（或上浮）时，会受到重力、浮力、摩擦力的作用。刚开始沉降（或上浮）时，因受重力作用产生加速运动，经过很短的时间后，颗粒的重力与水对其产生的阻力平衡时，颗粒即等速下沉。

影响因素：颗粒密度，水流速度，池的表面积。

考点：水污染控制工程水污染控制工程题库
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题型：阅读理解

In the United States, it is not usual to telephone someone early in the morning. If you telephone early in the day, while he is shaving or having breakfast, the time of the call shows that the matter is very important and requires immediate(立即的) attention. So it is with the telephone calls made after 11:00 pm. If someone receives a call during sleeping hours, he may think that it’s a matter of life and death. The time chosen for the call communicates its importance.

In social life, time plays a very important part. In the USA guests are likely to feel they are not highly regarded if the invitation to a dinner party reaches them only three or four days before the party date. But it is not true in all countries. In other areas of the world, it may be thought silly to make an appointment(约会) too far ahead because plans which are made for a date more than a week away may be forgotten. The meaning of time is not the same in different cultures that treat time differently; being on time is valued highly in American life, for example. If people are not on time, they may be regarded as impolite or not fully responsible(责任). In the USA no one would think of keeping a business friend for an hour; it would be too impolite. A person who is 5 minutes late is asked to make a shout apology (道歉). If he is less than 5 minutes late, he will say a few words of explanation(解释), though perhaps he will not complete the sentence.

小题1:A call at midnight would mean_________.

A．the matter is less important

B．the matter is too difficult to handle

C．the matter requires immediate attention

D．it is a matter of life and death小题2:According to the passage, time plays a very important part in__________.

A．everyday life

B．personal life

C．getting along with others

D．business小题3:In the passage, the writer suggests that invitation cards should be sent___________.

A．three or four days before the party date in all cultures

B．three or four days before the party date in some cultures

C．three or four days before the party date in the USA

D．at your chosen time
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