在数据库中能够唯一地表示一个元组的属性或者属性的组合成为( )。

未知题型

What accounts for the great outburst of major inventions in early America—breakthrough such as the telegraph, the steamboat and the weaving machine? Among the many shaping factors, I would single out the countrys excellent elementary schools; a labor force that welcomed the new technology; the practice of giving premiums to inventors; and above all the American genius for nonverbal, 'spatial' thinking about things technological. Why mention the elementary schools? Because thanks to these schools our early mechanics, especially in the New England and Middle Atlantic states, were generally literate and at home in arithmetic and in some aspects of geometry and trigonometry. Acute foreign observers related American adaptiveness and inventiveness to this educational advantagE.As a member of a British commission visiting here in 1853 reported, 'With a mind prepared by thorough school discipline, the American boy develops rapidly into the skilled workman. ' A further stimulus to invention came from the 'premium' system, which preceded our patent system and for years ran parallel with it. This approach, originated abroad, offered inventors medals, cash prizes and other incentives. In the United States, multitudes of premiums for new devices were awarded at country fairs and at the industrial fairs in major cities. Americans flocked to these fairs to admire the new machines and thus to renew their faith in the beneficence of technological advancE.Given this optimistic approach to technological innovation, the American worker took readily to that special kind of nonverbal thinking required in mechanical technology. As Eugene Ferguson has pointed out, 'A technologist thinks about objects that cannot be reduced to unambiguous verbal descriptions; they are dealt with in his mind by a visual, nonverbal process.... The designer and the inventor... are able to assemble and manipulate in their minds devices that as yet do not exist. ' This nonverbal 'spatial' thinking can be just as creative as painting and writing. Robert Fulton once wrote, 'The mechanic should sit down among levers, screws, wedges, wheels, etC., like a poet among the letters of the alphabet, considering them as an exhibition of his thoughts, in which a new arrangement transmits a new ideA.' When all these shaping forces—schools, open attitudes, the premium system, a genius for spatial thinking—interacted with one another on the rich U. S. mainland, they produced that American characteristic emulation. Today that word implies mere imitation. But in earlier times it meant a friendly but competitive striving for fame and excellencE.Questions:
According to the author, the great outburst of major inventions in early America was in a large part due to______.
A.elementary schools
B.enthusiastic workers
C.the attractive premium system
D.a special way of thinking

未知题型

Most people agree that taxes must be paiD.Government couldnt run without money. So people dont argue against taxes. They just argue about how taxes should be collecteD.At present the federal government works with a 'progressive tax'. The tax covers a percentage of peoples wages. Not everyone pays the same percentage of his salary in taxes. Taxpayers fall into different 'tax brackets' depending on their incomE.Poor people are in a low tax bracket. They pay the smallest percentage of income in taxes. Middle income workers pay a larger percentage than the poor. And the rich fall into the high tax brackets. Few rich people like the progressive tax. The government took a poll. Among other people, the government talked to Ray Mathers and Eve Winick. 'Lets change to a flat rate tax,' says Ray Mather. 'Everyone should be taxed the same percentagE.Its fair. And its easy to figure out. ' Mathers is president of Trig Computer Company. He makes over $ 80 000 a year. 'I dont want a flat rate income tax,' says Eve Winick. Winick is a grammar school teacher. Her school is in a poor neighborhooD.She makes $ 14 000 a year. 'I dont care if its easier to figure out. What I want to know is, would I pay less tax?' Winick worries about her students parents. 'Some of them can hardly support themselves. Why should they pay heavier taxes? Theyre the people who need government services. ' Mathers thinks a flat rate would help in the long run. 'The country could lower taxes after a whilE.See, if I paid fewer taxes, Id save money. Id put that money into my business and hire more peoplE.Those people could pay taxes. Everybody would be better ofF.' Questions:
According to the progressive tax, who should pay the highest percentage of their income in taxes?
A.The rich.
B.The poor.
C.The middle class.
D.The lower class.

单项选择题

图

A．充分条件
B．必要条件
C．充分必要条件
D．既不充分也不必要条件

在数据库中能够唯一地表示一个元组的属性或者属性的组合成为( )。 A.
记录 B.
字段 C.
域 D.
关键字

相关考题

在数据库中能够唯一地表示一个元组的属性或者属性的组合成为( )。 A. 记录 B. 字段 C. 域 D. 关键字

相关考题

在数据库中能够唯一地表示一个元组的属性或者属性的组合成为( )。 A.
记录 B.
字段 C.
域 D.
关键字