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Bacteria （细菌) are extremely small living things. While we measure our own sizes in inche

Bacteria (细菌) are extremely small living things. While we measure our own sizes in inches or centimeters, bacterial size is measured in microns. One micron is a thousandth of a millimeter: a pinhead is about a millimeter across. Rod-shaped bacteria are usually from two to four microns long, while rounded ones are generally one micron in diameter. Thus, if you enlarged a rounded bacterium a thousand times, it would be just about the size of a pinhead. An adult human magnified by the same amount would be over a mile (1.6 kilometers) tall.

Even with an ordinary microscope, you must look closely to see bacteria. Using a magnification of 100 times, one finds that bacteria are barely visible as tiny rods or dots. One cannot make out anything of their structure. Using special stains, one can see that some bacteria have attached to them wavy-looking "hairs" called flagella. Others have only one flagellum. The flagella rotate, pushing the bacteria through the water. Many bacteria lack flagella and cannot move about by their own power, while others can glide along over surfaces by some little-understood mechanism.

From the bacterial point of view the world is a very different place from what it is to humans.To a bacterium water is as thick as molasses (糖蜜) is to us. Bacteria are so small that they are influenced by the movements of the chemical molecules around them. Bacteria under the microscope even those with no flagella often bounce about in the water. This is because they collide with the water molecules and are pushed this way and that molecules move so rapidly that within a tenth of a second the molecules around a flagellum have been replaced by new ones. Even bacteria without flagella are thus constantly exposed to a changing environment.

Which of the following is the main topic of the passage？

A．The characteristics of bacteria.

B．How bacteria reproduce.

C．The various functions of bacteria.

D．How bacteria contribute to disease.

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更多“Bacteria （细菌) are extremely sm…”相关的问题

第1题

Forty-thousand of the world’s young children die every day. Many of these deaths can be pr

evented. In fact, experts say, techniques now exist to save the lives of half of these children. The techniques are medically effective(有效的), simple to use and low cost. The biggest task has been to inform. parents 'about these life-saving techniques.

Diarrhea(腹泻) is the main cause of death among children in developing countries. Diarrhea results when the body tries to clear itself of harmful bacteria (细菌). The body does this by getting out liquids, sometimes uncontrollably. If too much water, sugar and salt are lost in this way, the body cannot work normally. The child may die.

The United Nations International Children's Fund, UNICF, introduces a technique. It uses a simple mixture of sugar and salt in water. The mixture does not stop diarrhea. But if used often as needed, it keeps fluid (体液) levels normal until the body has fought off the harmful bacteria.

In Egypt, for example, the treatment was used in a children’s health care program in the province of Alexandria. It reduced by one-half the number of deaths caused by diarrhea. The technique has now been used throughout tile country.

According to the passage, a large number of Children can be saved only when ______.

A．the life-saving ways are medically effective

B．their parents are rich enough for the life-saving techniques

C．the life-saving techniques are easy to use

D．their parents learn the life-saving techniques

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第2题

Milk was one of the main foods for people long before history was written.Maybe【21】will re

Milk was one of the main foods for people long before history was written. Maybe【21】will remain an important food as long as there are【22】that give milk. The old word "milk"【23】Sanskrit(梵文), one of the oldest【24】known to man. A very old picture of milking,【25】was drawn five thousand years ago, has been found.

In the years long ago, people got their milk【26】their own animals. But【27】modern times new inventions made the milk industry(产业) a big business.【28】1851 Gall Borden found a way to【29】some of the water out from milk. This made milk keep longer. Four years later, Louis Pasteur【30】 a way to kill the bacteria(细菌) in milk. Then a special milk bottle was made. This was followed【31】 the invention of machines that could fill bottles with milk. The discoveries had a great effect(影响) on the milk industry. They meant that milk could be kept longer.

Some people believe that milk drinking will become less popular【32】 it has been. But remember how long milk has been an important food【33】 think of the many ways【34】 it is useful. It seems【35】 to say that the milk industry will always be important.

(36)

A．it

B．they

C．he

D．she

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第3题

In paragraph 3, sentence 2, the author compares water to molasses in order to introduce wh

ich of the following topics？

A．The bacterial content of different liquids.

B．What happens when bacteria are added to molasses.

C．The molecular structures of different chemicals.

D．How difficult it is for bacteria to move through water.

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第4题

A．areaB．appealC．bacteriaD．cafeteria

A.area

B.appeal

C.bacteria

D.cafeteria

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第5题

This passage is mainly about ______.A) the definition of bacteriaB) health germsC) pro

This passage is mainly about ______.

A) the definition of bacteria

B) health germs

C) probiotics

D) probiotics versus antibiotics

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第6题

The university has launched a research center to develop new ways of ______ bacteria which

have become resistant to drug treatments.

A．regulating

B．halting

C．interrupting

D．combating

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第7题

A. decade B. aggressive C. ancestor D. bacteria

A. decade

B. aggressive

C. ancestor

D. bacteria

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第8题

When the mixture is used, it is important to______.A．keep sugar and salt in waterB．drink i

When the mixture is used, it is important to______.

A．keep sugar and salt in water

B．drink it as often as necessary

C．take it as much as possible

D．use it to kill the bacteria

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第9题

According to the passage, someone who examines bacteria using only a microscope that magni

fies 100 times would see ______.

A．tiny dots

B．small "hairs"

C．large rods

D．detailed structures

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第10题

According to this passage, ______may result in the imbalance of bacteria in your intes

tines.

A) antibiotic treatment for an ear infection

B) taking pills which contain freeze-dried germs

C) eating yogurt or buttermilk

D) eating products made from fermented milk

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