问题 单项选择题

下面关于PC机输入/输出控制的叙述中,正确的是 ( )

A.程序控制方式是指在程序的控制下进行数据传送,这是微处理器与外围设备之间交换信息的一种最简单的方式,可分为无条件传送方式和条件传送方式

B.PC机输入/输出控制有三种方式:程序控制方式、中断控制方式及DMA控制方式,尽管这三种方式各有特点,但都必须通过CPU执行指令来完成具体的数据传送

C.从总体上来说,中断控制方式的效率高于DMA控制方式

D.一般中断控制方式的效率高于程序控制方式,但是系统有n个中断源时,CPU本身就必须有n个中断引脚,这是中断方式的一个缺点

答案

参考答案:A

解析: 程序控制方式是指CPU与外设间的数据传送是在程序的控制下完成的一种数据传送方式。这种方式又分为无条件传送和条件传送两种。所以选项A正确。输入/输出控制方式有三种方式:程序控制方式、中断控制方式以及DMA控制方式。DMA控制方式传输速度快,适合于成批数据传送,只在传送开始和结束时需要CPU参与,数据传送过程中无须 CPU干预,提高了CPU的效率,中断控制方式中断次数多,CPU仍需要花较多的时间处理中断,能够并行操作的设备台数也受到中断处理时间的限制,中断次数据增多导致数据丢失。所以其他选项都是错误的。

单项选择题
单项选择题

Actually, though, America, the "land of immigrants", has always had people of many different nationalities and languages. The 1990 census indicates that almost 14% of Americans speak a non English language at home. Yet only 3% reported that they spoke English "not well" or "not at all". That means that slightly more than one out of 10 Americans could be considered bilingual.

Besides that, many high school, college students, and even some elementary school students are required to take a foreign language as a part of their curriculum. In addition to old standbys like Spanish, German and French, more and more students are opting for Eastern European and Asian languages. Of course, not all students keep up their foreign language abilities. As the old saying goes, " If you don’t use it. " But still, a growing number of Americans are coming to appreciate the benefits of being multilingual.

Ethnic enclaves, found particularly in major metropolitan centers, have preserved the language and culture of American immigrants. Some local residents can function quite well in their native language, without having to bother learning English. Regions such as southern Florida and the Southwest have numerous Spanish speaking neighborhoods. In fact, Spanish speakers—numbering over 17 million—compose the largest non English linguistic group in America. But Chinese, Vietnamese, Italian, Polish and many other ethnic group add to the linguistic flavor of America. Foreign languages are so commonly used in some ethnic neighborhoods that visitors might think they are in another country!

Although some Americans welcome this linguistic and cultural diversity, others have begun to fear that the English language is being threatened. Since the 1980s, the "English Only" movement has sought to promote legislation which would establish English as the "official language" and restrict the use of non English language. However, some groups, including TESOL, the organization for Teachers of English to Speakers of Other Language, object to such "language restrictionism". Their view, known as "English Plus", suggests that Americans should have respect for people’s native language and help them fit into the mainstream of society. But so far, 19 states have passed English Only legislation, and the topic is the focus of an ongoing debate.

Whether or not English is the official language of the United States, it remains the "language of wider communication". Nearly everyone recognizes the need to develop proficiency in English in order to do well in America. To help those who want to brush up on their English skills, English as a Second Language (ESL) classes around. Cities with large numbers of recent immigrants often set up bilingual education programs to teach students content subjects in their native language while they improve their English. Language educators often have p and divergent views as to which approach helps learners achieve better results: a bilingual approach, an ESL approach or even a pure immersion ("sink or swim") approach. However, all these teachers share a common commitment: to help students function well in English.

Americans recognize that English is the international language, and people with good English skills can get by in many international settings. On the other hand, in a world growing increasingly smaller, second language skills can be a great favor. They can build cross cultural bridges and give people an edge in a variety of career field. Indeed, lack of foreign language proficiency can limit one’s chances for advancement and keep one in a cultural dead end street. As many people in America are discovering, being monolingual is no laughing matter.

Foreign languages are commonly used in some ethnic neighborhoods because ().

A.ethnic groups have preserved their native languages

B.ethnic groups are not allowed to speak English

C.ethnic groups encourage their natives to learn foreign languages

D.ethnic groups allow their natives to go to another country