一般认为正常情况下二沉池泥层距水面为0.5-1m。

在使用无线技术时，下面（）比较有效而且很难截取。

A.码分多址CDMA

B.时分多址TDMA

C.公共交换电话网

D.微型终端/小型卫星地球

我国实行的计划单列市制度，是我国城市经济体制改革的产物。计划单列提高了大区域性中心城市和重要沿海开放城市在国家管理组织体系中的层位，使之与这些城市的经济规模、经济地位和经济功能大体相适应，从而为进一步实现按照市场经济要求和社会化大生产来组织管理经济创造了条件。因此( )。

A．应当进一步完善城市计划单列

B．应当提高中心城市和开放城市的地位

C．要借鉴研究国外计划单列市的有关经验

D．要深化城市改革

[A] A machine has been developed that pulps paper and then processes it into packaging, e.g. egg-boxes and cartons. This could be easily adapted for local authorities use. It would mean that people would have to separate their refuse into paper and non-paper, with a different dustbin for each. Paper is, in fact, probably the material that can be most easily recycled; and now, with massive increases in paper prices, the time has come at which collection by local authorities could be profitable.

[B] Recycling of this kind is already happening with milk bottles, which are returned to the dairies, washed out, and refilled. But both glass and paper are being threatened by the growing use of plastic. More and more dairies are experimenting with plastic bottles, and it has been estimated that if all the milk bottles necessary were made of plastic, then British dairies would be producing the equivalent of enough plastic tubing to encircle the earth every five or six days!

[C] The package itself is of no interest to the shopper, who usually throws it away immediately. Useless wrapping accounts for much of the refuse put out by the average London household each week. So why is it done Some of it, like the cellophane on meat, is necessary, but most of the rest is simply competitive selling. This is absurd. Packaging is using up scarce energy and resources and messing up the environment.

[D] The trouble with plastic is that it does not rot. Some environmentalists argue that the only solution to the problem of ever growing mounds of plastic containers is to do away with plastic altogether in the shops, a suggestion unacceptable to many manufacturers who say there is no alternative to their handy plastic packs.

[E] Little research, however, is being carried out on the costs of alternative types of packaging. Just how possible is it, for instance, for local authorities to salvage paper, pulp it and recycle it as egg-boxes Would it be cheaper to plant another forest Paper is the material most used for packaging--20 million paper bags are apparently used in Great Britain each day--but very little is salvaged.

[F] It is evident that more research is needed into the recovery and re use of various materials and into the cost of collecting and recycling containers as opposed to producing new ones. Unnecessary packaging, intended to be used just once, and making things look better so that more people will buy them, is clearly becoming increasingly absurd. But it is not so much a question of doing away with packaging as using it sensibly. What is needed now is a more sophisticated approach to using scarce resources for what is, after all, a relatively unimportant function.

[G] To get a chocolate out of a box requires a considerable amount of unpacking: the box has to be taken out of the paper bag in which it arrived; the cellophane wrapper has to be torn off, the lid opened and the paper removed; the chocolate itself then has to be unwrapped from its own piece of paper. But this insane amount of wrapping is not confined to luxuries. It is now becoming increasingly difficult to buy anything that is not done up in cellophane, polythene or paper.

Order:

41（）

下题基于“学生—选课—课程”数据库中的三个关系：
S(S#,SNAME,SEX,AGE)，
SC(S#,C#,GRADE)，
C(C=#,CNAME,TEACHER)
它们的主码分别是S#，(S#，C#)和C#。

设S_AVG(SNO，AVG_GRADE)是一个基于SC表定义学生号和他的平均成绩的视图。下面对该视图的操作语句中，哪个(些)不能正确执行______。
Ⅰ．UPDATE S_AVG SET AVG_GRADE=90 WHERE SNO=’2004010601’;
Ⅱ．SELECT SNO，AVG_GRADE FROM S_AVG WHERE SNO=’2004010601’;
Ⅲ．INSERT INTO S_AVG VALUES(’2004010618’，88);

A．仅Ⅰ和Ⅲ
B．仅Ⅱ
C．仅Ⅱ和Ⅲ
D．都不能

在火灾危险等级分类中，（）一般指可燃物品较少、火灾放热速率较低、外部增援和人员疏散较容易的场所。

A.轻危险级

B.中危险级

C.严重危险级

D.仓库火灾危险级