关于环状拓扑的特点,说法错误的是______。A.在环形拓扑结构中,节点通过点对点通

题型:单项选择题

问题:

关于环状拓扑的特点,说法错误的是______。

A.在环形拓扑结构中,节点通过点对点通信线路连接成闭合环路

B.环状拓扑结构简单,传输延时确定

C.保证环的正常运行,只需要简单的环维护处理

D.环中数据将沿一个方向逐站传送

考点:计算机等级考试网络技术三级网络技术笔试97
题型:单项选择题

自来水是我国目前生活饮用水,下表是我国颁布的生活饮用水水质标准的部分内容.

项目标准
感官指标无异味、异臭等
化学指标pH6.5-8.5,铜<1.0mg•L-1,铁<0.3mg•L-1,氟化物<1.0mg•L-1,游离氯≥0.3mg•L-1等
(1)感官指标表现的是自来水的______性质(填“物理”或“化学”);若化学指标中的pH=8时,表明自来水呈______(填“酸性”、“碱性”或“中性”).

(2)自来水属于______(填“纯净物”或“混合物”); 自来水中的游离氯有少量可转变成氯离子,氯离子的符号是______.

(3)实验室用自来水制取蒸馏水的方法是______.

A.吸附    B.沉淀   C.过滤   D.蒸馏

(4)长期饮用蒸馏水______(填“利于”或“不利于”)人体健康.

(5)区别软水和硬水的方法是在水样中加入______;可以通过______或______方法把硬水变成软水.

题型:单项选择题

阅读理解。

                                                  How to wash clothes in a flash

     LAUNDRY is never an easy part of housework. But if piles of sweaty (汗水浸湿的) T-shirts and

smelly socks drive you crazy, then two Chinese scientists might have the answer.

    Long Mingce and Wu Deyong of Shanghai Jiao Tong University have invented a kind of cotton that

cleans itself. No need for soap or water, the scientists say. All you have to do is put the clothes out in the

sun.

    According to the Guardian, this magical self-cleaning ability comes from a special chemical mixture.

The material is covered with this mixture. It can break down dirt and remove bad smells after only a few

hours in the sun.

    One of the chemicals is called titanium dioxide (二氧化钛). Scientists have known for some time that

titanium dioxide can clean fabrics (织物). However , it only works under ultraviolet (紫外的) light and so

is not yet widely used - ultraviolet light cannot be seen.

   "We knew that self-cleaning cotton fabrics with titanium dioxide coating had already been developed,

but they cannot work, or they work weakly, under sunlight," Long said. "If we want to use the fabrics in

daily life, we must develop cotton that cleans itself under daylight."

   The scientists worked hard for years to find a better chemical. Finally , they added silver iodide (碘化银) into the mixture. This made the chemical reactions in sunlight faster. The new mixture is also nearly

seven times better than the former one with pure titanium dioxide at removing dirt and killing bacteria.

   The experiment was only carried out on cotton clothing. However, according to Long, the technology

can be "applied to all kinds of fabrics and their related products." It is also cheap and environmentally

friendly , he said.

   The self-cleaning material is not yet ready for the market. Scientists still need to know whether it could

harm people. Although titanium dioxide is used in some foods, it can cause health problems if it gets into

the lungs (肺). Scientists need to make sure it is safe before we can start to enjoy the benefits of this

technology .

1. Thanks to this new discovery, we will be able to clean fabrics ___ .

A. using soap and water  

B. using silver iodide  

C. using sunlight        

D. using moonlight

2. In what way is the new material better than previous materials ?

A. It works using any kind of light.  

B. It works more quickly and effectively.

C. It is widely found in nature.      

D. It can be used for all kinds of fabrics .

3. What might be a problem with the self-cleaning material ?

A. It will cause pollution.          

B. It costs too much to produce.

C. It breaks down easily in the sun.  

D. It might cause health problems

4. Which of the following statements is TRUE? 

A. There may be many other kinds of self-cleaning fabric in the future .

B. We can already buy self-cleaning clothes on the market.

C. This was the first time that scientists discovered titanium dioxide.

D. Titanium dioxide is widely used in the food industry.

题型:单项选择题

急性脓耳,脓液黄稠量多,多为胃火犯耳证或脾胃湿热熏耳证。

题型:单项选择题

急性筋伤病理变化的三期划分及发展演变规律是什么?

题型:单项选择题

道路运输驾驶员应树立()的思想。

A.争抢客源可以获得更大效益

B.安全就是效益

C.经济利益大于一切

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