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[主观题]

Scientists have known for some time that certain plants, called hyperaccumu-lators, can co

ncentrate minerals at levels a hundredfold or greater than normal. A survey of known hyperaccumulators identified that 75 percent of them amassed nickel; cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of choice. Hyperaccumulators run the entire range of the plant world. They may be herbs, shrubs, or trees. Many members of the mustard family, spurge family, legume family, and grass family are top hyperaccumulators. Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of metals may afford some protection against plant-eating insects and microbial pathogens.

Why does the author mention "herbs," "shrubs," and "trees"？

A．To provide examples of plant types that cannot tolerate high levels of harmful minerals

B．To show why so many plants are hyperaccumulators

C．To help explain why hyperaccumulators can be found in so many different places

D．To emphasize that hyperaccumulators occur in a wide range of plant types

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发布时间：2019-10-13

更多“Scientists have known for some time that certain plants, called hyperaccumu-lators, can co”相关的问题

第1题

What have scientists come to know recently about formation of life？

What have scientists come to know recently about f

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第2题

Scientists are responsible for people who hold harmful beliefs about human nature because.

A．the theories of scientists are used as justification for such harmful beliefs

B．only through science can these people be refuted

C．they have an obligation to correct their mistakes

D．scientists are the ones who know the true nature of humankind

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第3题

From the passage we know that the author__________ A．thinks that scientists are ab

From the passage we know that the author__________

A．thinks that scientists are about to achieve artificial intelligence

B．doubts whether scientists can ever achieve artificial intelligence

C．does not think that scientists have found real artificial intelligence

D．is sure that scientists have achieved artificial intelligence.

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第4题

A. seem to know how to control laughter B. reduce your blood pressureC. why people laugh D

A. seem to know how to control laughter B. reduce your blood pressure

C. why people laugh

D. the intake and release of air

E. the purpose of laughter is to reduce stress

F. the way it affects the immune system

Scientists do not have clear evidence as to______

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第5题

The passage supplies information for answering which of the following questions？A．Where wa

The passage supplies information for answering which of the following questions？

A．Where was the mechanism made？

B．What was the primary purpose of the Antikythera mechanism？

C．How did ancient scientists know how to use the Antikythera mechanism？

D．Precisely how many gears did the mechanism have？

E．What is the purpose of computer tomography？

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第6题

听力原文：Man has a big brain. He can think and speak. Scientists used to think that men ar

听力原文： Man has a big brain. He can think and speak. Scientists used to think that men are different from animals because they can think and learn. They now know that animals can learn —dogs, rats, birds —and worms —can learn. So scientists are beginning to understand that men are different from animals because they can speak. Animals cannot speak. They make noises when they are afraid, or angry, or unhappy. Apes are our nearest cousins. They can understand some things more quickly than human beings, and one or two have learned a few words. But they are still different from us. They cannot join words and make sentences. They cannot think like us because they have no language. They can never think about the past or the future.Language is a wonderful thing. Man has been able to develop civilization because he has language. Every child can speak his own language very well when he is four or five —but no animal learns to speak. How do children learn？ Scientists do not really know. What happens when we speak？ Scientists do not know. They only know that man can speak because he has a big brain.

(34)

A．Because he has a big brain.

B．Because he learns to speak.

C．Because he develops civilization.

D．Because he knows many words.

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第7题

Have you ever suddenly felt that someone you know was in trouble-and he was？ Have you ever

dreamed something that came true later？ Maybe you have ESP(超感官知觉).

ESP stands for Extra Sensory Perception. It may be called a sixth sense. It seems to let people know about events before they happen, or events that are happening some distance away.

Here is an example: A woman was doing washing. Suddenly she screamed. "My father is dead! I saw him sitting in the chair!' Just then, a telegram came. The woman's father had died of a heart attack. He died sitting in a chair.

There are thousands of stories like this on record. Scientists are studying them to find out what is behind these strange mental messages. Here's another example--one of hundreds of dreams that have come true.

A man dreamed he was walking along a road when a horse and carriage came by. The driver said, "There's room for one more." The man felt the driver was Death, so he ran away. The next day the man was getting on a crowded bus. The bus driver said, "There's room for one more." Then the man saw the driver's face was the same face he had seen in the dream. He wouldn't get on the bus. As the bus drove off, it crashed and burst into flames. Everyone was killed!

Some people say stories like these are lies or coincidences. Others, including some scientists say that ESP is true. From studies of ESP, we may some day learn more about the human mind.

ESP lets people know about

A．their dreams

B．events after they happen

C．events before they happen

D．heart attacks

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第8题

Mike: Why haven't more women chosen careers in science？ Alice: Well, first of all, most ch

ildren grow up with the idea that boys understand science more easily than girls do. This continues in the high school and college years. Later, it's hard for a woman to get a job in science. Mike: ______ Alice: Well, no, I didn't. A career doesn't get in the way. My husband and children try to understand my work and they are willing to help me. I know many women scientists who have happily arrived and have families.

A．Did you sacrifice a family for your work？

B．Did you feel happy with your life？

C．Did you have something interesting to share with us？

D．Did you get a higher salary？

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第9题

Scientists are learning more about our need for sleep. Most people sleep 【26】______ eight

hours each night. 【27】______ people sleep more than 【28】______ and others sleep as 【29】______ as two or three hours each night. Scientists do not know exactly 【30】______ some people sleep more than others. Dr. Ernest Hartman has a(an) 【31】______ about this. He believes that the 【32】______ of sleep depends on how a person 【33】______ problems. He said people who need only a few 【34】______ sleep usually are people who have much energy and make good use of 【35】______ to get their work to be done quickly. 【36】______ he said many people who sleep longer than normal do creative work and seem to need 【37】______ dreaming time to find solution 【38】______ emotional problems. Some scientists agree 【39】______ this idea and others dispute.

To determine the 【40】______ of the lack of sleep, scientists have put 【41】______ through a set of psychological and performance tests 【42】______ them, for instance, to add columns of numbers or recite a passage read to them only minutes earlier, "We've found that if you're in sleep 【43】______ , performance suffers," says Dr. David. "Short-term memory is 【44】______ , 【45】______ are abilities to make decisions and to concentrate."

【26】

A．for

B．at

C．in

D．since

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第10题

Natural Medicines Since earliest days, humans have used some kinds of medicines. We know t

Natural Medicines

Since earliest days, humans have used some kinds of medicines. We know this because humans have survived. Ancient treatments for injury and disease were successful enough to keep humans from dying out completely.

They were successful long before the time of modern medicine. Before the time of doctors with white coats and shiny (发亮的) instruments. Before the time of big hospitals with strange and wonderful equipment.

Many parts of the world still do not have university-educated doctors. Nor do they have expensive hospitals. Yet injuries are treated. And diseases are often cured. How？ By ancient methods. By medicines that might seem mysterious, even magical (有魔力的). Traditional medicines are neither mysterious nor magical, however.

Through the centuries, tribal (部族的) medicine men experimented with plants. They found many useful chemicals in the plants. And scientists believe many of these traditional medicines may provide the cure for some of today's most serious diseases.

Experts say almost 80% of the people in the world use plants for health care. These natural medicines are used not just because people have no other form. of treatment. They are used because people trust them. In developed areas, few people think about the source of the medicines they buy in a store. Yet many widely-used medicines are from ancient sources, especially plants. Some experts say more than 25% of modern medicines come, in one way or another, from nature.

Scientists have long known that nature is really a chemical factory. All living things contain chemicals that help them survive. So scientists' interest in traditional medicine is not new. But it has become an urgent concern. This is because the earth's supply of natural medicines may be dropping rapidly.

The passage indicates that ancient treatments for injury and disease were

A．much more successful than modern ones.

B．successful enough for humans to survive.

C．successful in all cases.

D．of little help to humans.

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