如果对一个关系实施了一种关系运算后得到了一个新的关系，而且新的关系中的属性由该运算决定，这说明所实施的运算关系是：(3)。

(75)

(74)

(72)

(73)

(70)

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

 In recent years, there has been a dramatic increase in the range of media used to(71)information. Initially, communication was limited to simple forms of(72)such as voice and paper. This century, however, has witnessed the introduction of a greater variety of media types such as the telephone and visual forms of media. In the latter part of the century, this trend has accelerated and there is now a wide range of media types available to convey information. These advances provide a great opportunity for new developments in a range of areas such as education and commerce. However, there are also a number of problems associated with the growth of(73)in society. In particular, there is a great danger of creating information(74). This problem can be seen, for example, in business where executives are required to make decisions based on an ever increasing variety and volume of information.(75)problems are also occurring in areas such as government, health care and education.

(68)

(69)

For each blank, choose the best answer from the four choices and write down on the answer sheet.

 When we just had text on screen, the basic user interface was a DOS(66)or maybe a simple list of choices. Now that we have graphics and text at the same time, we can have a much mom intuitive mouse - driven graphics based user interface with(67)menus, as in the Macintosh, Microsoft Windows, and Presentation Manager. When we can add photograph - quality images, animation, good -quality sound, and interactivity, then we ought to be able to make computers much more powerful - and much easier to use. That's tile concept behind(68), the newest buzzword. Multimedia, which typically refers to a synthesis of graphics, animation, optical storage, image processing, and sound, is not a single technology, product, or market. Instead, it is a collection of technologies that proponents believe will one day be joined together. So far, most of the activity in Multimedia has taken place on the Macintosh and on the Amiga because of their(69)graphics and sound features but you can expect this technology to spread to other(70)

(67)