问题 问答题 简答题

什么是液压系统的职能符号?职能符号的作用是什么?

答案

参考答案:

液压系统是由各种元件组成的。一个系统中往往要使用很多不同功能的元件,并由管路把它们连接起来,如果用结构图表达,往往是元件纵横排列、管道来往交错,即看不清楚,绘制又很麻烦。因而采用了一定的图形符号来简便清楚地表达各种元件和管道,这种图形符号称职能符号。

职能符号只能表达元件的作用、原理而不能反映元件的结构。用图形符号绘制的职能符号液压系统图,简便直观。

单项选择题
阅读理解

The relationship between humans and animals has always been complex. Some cultures have developed entire belief systems around favored animals. Even in cultures with less formal belief systems, connections between people and animals still lead to commonly accepted opinions about animals.

These belief systems usually develop around the animals that interact (互动) with humans most frequently. Therefore, it should not be surprising that so many stories surround the most common of animals: rats. Rats live side by side with humans all over the world and regularly interact with people. Human-rat coexistence may be common all around the world, but different cultures respond to that closeness in different ways.

In the United States and Europe, one typical attitude is that the rat is a pest. This could be due to the common belief that rats spread disease. Actually, they don’t, at least not directly, but many people don’t know that. The Pied Piper of Hamlin, a well-known children’s story, is one example of how rats have been described in Western literature: in that story, rats cause such a problem that a town has to hire a piper to call them all away.

In many Latin American countries, the rat is described in a very different way. The story of the tooth fairy (a fairy believed by children to leave money while they sleep in exchange for a tooth that has come out) is common all over the world, but in Latin America, the “fairy” is a rat! Rats do have very strong teeth, which could explain the association. Clearly, this shows another attitude toward rats that is much more positive.

Yet another attitude toward the rat can be seen in the Chinese Zodiac (生肖). The Rat is one of the animals of the Zodiac. Like the other zodiac animals, the Rat is neither entirely good nor entirely bad. It’s described as clever and friendly, but also tricky and not entirely honest. That may be the most accurate description of the rat so far. Whether you like rats or not, it’s hard to deny their reputation for cleverness.

As many people are discovering these days, rats can even make excellent pets, so long as you remember to close the cage carefully!

小题1:What does the passage mainly talk about?

A.A trend of keeping rats as pets.

B.How different cultures look at rats.

C.How humans get along with animals.

D.Favored animals in different cultures.小题2:The rats in The Pied Piper of Hamlin appear______.

A.unpleasant

B.honest

C.smart

D.unusual小题3:The tooth fairy in Latin America mentioned in Paragraph4 is to show______.

A.the tooth fairy is lovely

B.rats look very frightening

C.rats are welcome in Latin American countries

D.the story of the tooth fairy is common all over the world小题4:According to the author, rats______.

A.don’t spread disease

B.should be treated as pests

C.are fairly described in the Chinese Zodiac

D.are kept as pets by more and more people小题5:The passage is probably taken from a ______.

A.travel guide

B.news report

C.nature magazine

D.history textbook