问题 单项选择题

能将模拟信号转换成数字信号的电路称为()。

A.电流转换器

B.电压转换器

C.数模转换器

D.模数转换器

答案

参考答案:D

解析:

实际中遇到的信号多是模拟量,要处理这些信号必须首先将这些模拟信号转换成数字信号,经计算机分析处理后输出的数字量,也需要转换成模拟量才能为执行机构所接收。这样就需要一种能在模拟信号与数字信号之间起桥梁作用的电路,模数转换器和数模转换器。能将模拟信号转换成数字信号的电路称为模数转换器。

[点评] 本题考察的知识点是模数转换器和数模转换器。

填空题
单项选择题

In 1998 consumers could purchase virtually anything over the Internet. Books, compact discs, and even stocks were available from World Wide Web Sites that seemed to spring up almost daily. A few years earlier, some people had predicted that consumers accustomed to shopping in stores would be reluctant to buy things that they could not see or touch in person. For a growing number of time-starved consumers, however, shopping from their home computer was proving to be a convenient alternative to driving to the store.

A research estimated that in 1998 US consumers would purchase $ 7.3 billion of goods over the Internet, double the 1997 total. Finding a bargain was getting easier, owing to the rise of online auctions and Web sites that did comparison shopping on the Internet for the best deal.

For all the consumer interest, retailing in cyberspace was still a largely unprofitable business, however. Internet pioneer Amazon. com, which began selling books in 1995 and later branched into recorded music and videos, posted revenue of $153.7 million in the third quarter, up from $37.9 minion in the same period of 1997. Overall, however, the company’s loss widened to $45.2 million from $9.6 million, and analysts did not expect the company to turn a profit until 2001. Despite the great loss, Amazon. com had a stock market value of many billions, reflecting investors’ optimism about the future of the industry.

Internet retailing appealed to investors because it provided an efficient means for reaching millions of consumers without having the cost of operating conventional stores with their armies of salespeople. Selling online carried its own risks, however. With so many companies competing for consumers’ attention, price competition was intense and profit margins thin or nonexistent. One video retailer sold the hit movie Titanic for $9.99, undercutting the $19.99 suggested retail price and losing about $6 on each copy sold. With Internet retailing still in its initial stage; companies seemed willing to absorb such losses in an attempt to establish a dominant market position.

"For all the consumer interest"(Paragraph 3)means()

A. to the interest of all the consumers

B. for the interest of all the consumers

C. all the consumers are much interested

D. though consumers are very much interested