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问题 单项选择题


下面列出的条目中，哪些是数据库系统的组成成员 Ⅰ．操作系统 Ⅱ．数据库管理系统 Ⅲ．用户 Ⅳ．数据库管理员 Ⅴ．数据库

A．Ⅱ、Ⅲ、Ⅳ和Ⅴ

B．Ⅱ、Ⅳ和Ⅴ

C．Ⅰ、Ⅱ、Ⅳ和Ⅴ

D．都是

答案

参考答案：D

解析： 数据库系统(DBS， Data Base System)是指在计算机中引入数据库后的系统构成。一般由数据库、操作系统、数据库管理系统(及其开发工具)、应用系统、数据库管理员和用户组成。对照本题的题干和选项可知，正确答案是选项D。

单项选择题

黑洞一直被认为是星体命运的终点，简单点儿说，当星体消耗完最后一丝能量的时候，要么分裂，然后被别的星球“吞食”；要么浓缩成一个可怕的黑点，“吞食”一切经过它的物质和能量。
黑洞是一种体积极小、质量极大的天体，具有强大的引力。黑洞是看不见的，因为它的引力大得不让光发射出去，也可以让经过那里的光消失在它的黑点里。从前，科学家只能通过测量黑点周围的环境来确认黑洞，直接测量黑洞被认为是不可能的。然而，最近科学家却测得了黑洞的声音。黑洞是个天生的低音歌手，它声音低得让人们无法用耳朵去欣赏，只能用专用的仪器才能探测到。
日前，科学家们利用X射线太空望远镜，探测到了英仙座星系团中央的一个超大质量黑洞所发出的声波。这个星系团距离地球约2.5亿光年。这个黑洞发出的声波频率只有人耳所能听到的最低声音的千万亿分之一，是迄今为止在宇宙中探测到的最低沉的声音。
科学家们对于宇宙中的特大黑洞能够发出上述声波并不感到意外。虽然黑洞会尽可能地吞食物质和能量，但它们也不是一毛不拔，科学家以前也探测到它们会发出低频率的电磁波。为什么黑洞会发声呢 这是因为黑洞不停地吸收靠近它的物质，吸进物质的同时，也会从中心向外产生两股方向分别相反的高速物质流。天文学家们说，正是这些高速物质流导致黑洞发出声波。
这个新发现为破解困扰天文学界多年的一个谜团提供了线索。科学家曾经发现，不少星团周围都包裹着大量的炽热气体。他们猜测，这些气体应该随着时间的推移渐渐冷却下来；温度下降后的气体，应该在星团中央附近形成低压，吸引周边的气体进入星团中央区，在这一过程中，应该可以形成数十亿个星体。然而，事实上并非如此。星系团中心包含的高温气体在近百亿年中，温度一直很高而不冷却，这种现象着实让天文学家们不得其解。科学家们解释说，星系团中的高温气体可能吸收了声波中的能量，从而使高温得以维持。这一过程涉及的能量之大，令人震惊——相当于1亿个星体同时爆炸产生的能量。他们说，如果这一推测属实，这将意味着：英仙座星系团中央的这个黑洞所发出的“歌声”，可能在长达2.5亿年的时间里都没有发生过变化。

文中画线处的“这一推测”的“这”是指什么

A．星团周围包裹着大量的炽热气体随着时间的推移而冷却

B．星系团中心包含的高温气体近百亿年一直很高并不冷却

C．一亿个星体同时爆炸产生了巨大的能量使高温得以维持

D．星系团中的高温气体吸收了声波中的能量使高温得以维持
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阅读理解

阅读理解。

    The food we eat seems to have a great effect on our health. Although science has made big steps in

making food more fit to eat, it has, at the same time, made many foods unfit to eat. Some research has

shown that perhaps eighty percent of human illness is related to food and forty percent of cancer is related

to food as well. That food is related to illness is not a new discovery. In 1945, some researchers realized

that things commonly used to keep colors in meats and other food additives caused cancer. Yet, these

additives remain in our food, and it is difficult to know which things on the wrappings of foods are helpful

or harmful. The additives which we eat are not all so direct. Farmers often give penicillin to their animals,

and because of this, penicillin has been found in the milk of cows. Sometimes similar things are supplied to

animals not for their health, but just to make a profit. 

    The farmers are simply trying to fatten the animals in order to get a higher price on the market. Although

some countries have tried to control such things, the practice continues.

1. According to this passage, we can know _____. [ ]

A. perhaps most of human illness is caused by what we eat

B. perhaps most kinds of cancer are related to what people eat

C. cancer was discovered in 1945

D. science has made food unfit to eat

2. Things that are used to keep colors in meats are _____. [ ]

A. harmful

B. useless

C. helpless

D. dangerous

3. All the additives _____. [ ]

A. are bright and colorless

B. are not bright and colorful

C. have indirect effects on our health

D. have direct effects on our health

4. People use additives _____.[ ]

A. to make food more unfit to eat

B. to improve the color and taste of the food

C. to change the color of the food

D. to take off the diseases of the food

5. Which of the following is NOT true? [ ]

A. Some wrappings of food are harmful.

B. Farmers try to make more money on the market by fattening their animals.

C. "The practice continues" means "things are still going on like that".

D. We needn't take care of what we eat.

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