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A．given off
B．put out
C．set off
D．used up
答案
更多“Every chemical change either results from energy being used to produce the change, or caus”相关的问题
第1题
A．given off
B．put out
C．set off
D．used up
第2题
听力原文： You can tell the age of a tree by counting its tings. But these records of a tree's life really say a lot more. Scientists are using tree tings to learn what's been happening on the sun's surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows, it adds a layer to its trunk, taking up chemical elements from the air. By looking at the elements in the rings from a given year, scientists can tell what elements were in the air that year.
Dr. Stevenson is analyzing one element, carbon—14, in rings from both living and dead trees. Some of the rings go back almost ten thousand years to the end of the Ice Age. When Stevenson followed the carbon--14 trail back in time, he found carbon—14 levels change with the intensity of solar burning. You see the sun has cycles. Sometimes it bums fiercely. At other times it's relatively calm. During the sun's violent periods, it throws off charged particles in fast moving streams, called solar winds. The particles interfere with the formation of carbon—14 on earth. When there is more solar wind activity, less carbon—14 is produced. Ten thousand years of tree rings show the carbon—14 level rises and falls about every four hundred and twenty years. The scientists concluded that solar wind activity must follow the same cycle.
(30)
A．To find out the origin of carbon- 14 on Earth.
B．To analyze the composition of different trees.
C．To look into the pattern of solar wind activity.
D．To examine the chemical elements in the Ice Age.
第3题
The【C1】______took a sharp upward leap with the invention of writing, but even【C2】______it remained painfully slow for several centuries. The next great leap forward【C3】______knowledge acquisition did not occur【C4】______the invention of movable type in the 15th century by Gutenberg and others.【C5】______to 1500, by the most optimistic【C6】______Europe was producing books at a rate of 1000 titles per year. This means that it【C7】______a full century to produce a library of 100,000 titles. By 1950, four and a half【C8】______later, the rate had accelerated so sharply that Europe was producing 120,000 titles a year.【C9】______once took a century now took only ten months. By 1960, a【C10】______decade later, the rate had made another significant jump,【C11】______a century's work could be finished in seven and a half months.【C12】______, by the midsixties, the output of books on a world【C13】______, Europe included, approached the prodigious(巨大的)figure of 900 titles per day.
One can【C14】______argue that every book is a net gain for the advancement of knowledge. Nevertheless we find that the accelerative【C15】______in book publication does, in fact, crudely【C16】______the rate at which man discovered new knowledge. For example, prior to Gutenberg【C17】______11 chemical elements were known. Antimony(锑)the 12th, was discovered【C18】______about the time he was working on his invention. It was fully 200 years since the 11th, arsenic(砒霜), had been discovered.【C19】______the same rate of discovery continued, we would by now have added only two or throe additional elements to the periodic table since Gutenberg.【C20】______, in the 450 years after his time, certain people discovered some seventy additional elements. And since 1900 we have been isolating the remaining elements not at a rate of one every two centuries, but of one every three years.
【C1】
A．knowledge
B．rate
C．development
D．accumulation
第4题
Passage Two
Questions 62 to 66 are based on the following passage.
Scientists have devised a way to determine roughly where a person has lived using a strand(缕) of hair , a technique that could help track the movements of criminal suspects or unidentified murder victims .
The method relies on measuring how chemical variations in drinking water show up in people’s hair.
“You’re what you eat and drink, and that’s recorded in you hair,” said Thure Cerling, a geologist at the University of Utah.
While U.S diet is relatively identical, water supplies vary. The differences result from weather patterns. The chemical composition of rainfall changes slightly as raid clouds move.
Most hydrogen and oxygen atoms in water are stable , but traces of both elements are also present as heavier isotopes (同位素) . The heaviest raid falls first .As a result, storms that form. over the Pacific deliver heavier water to California than to Utah.
Similar patterns exist throughout the U.S. By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair, scientists can construct a geographic timeline. Each inch of hair corresponds to about two months.
Cerling’s team collected tap water samples from 600 cities and constructed a mop of the regional differences. They checked the accuracy of the map by testing 200 hair samples collected from 65 barber shops.
They were able to accurately place the hair samples in broad regions roughly corresponding to the movement of raid systems.
“It’s not good for pinpointing (精确定位),” Cerling said . “It’s good for eliminating many possibilities.”
Todd Park, a local detective, said the method has helped him learn more about an unidentified woman whose skeleton was found near Great Salt Lake.
The woman was 5 feet tall. Police recovered 26 bones, a T-shirt and several strands of hair.
When Park heard about the research, he gave the hair samples to the researchers. Chemical testing showed that over the two years before her death, she moved about every two months.
She stayed in the Northwest, although the test could not be more specific than somewhere between eastern Oregon and western Wyoming.
“It’s still a substantial area,” Park said “But it narrows it way down for me.”
62. What is the scientists’ new discovery？
A) One’s hair growth has to do with the amount of water they drink.
B) A person’s hair may reveal where they have lived.
C) Hair analysis accurately identifies criminal suspects.
D) The chemical composition of hair varies from person to person.
第5题
【C1】
A．nature
B．fact
C．research
D．addition
第6题
M: Well, to begin with, I was surprised to find out there was so much going on in bones. I always assumed they were pretty lifeless.
W: Well, that's an assumption many people make. But the fact is bones are made of dynamic living tissue that requires continuous maintenance and repair.
M: Right. That's one of the things I found so fascinating about the article the way the bones repair themselves.
W: Ok. So can you tell us how the bones repair themselves？
M: Sure. See, there are two groups of different types of specialized cells in the bone that work together to do it. The first group goes to an area of the bone that needs repair. This group of cells produces the chemical that actually breaks down the bone tissue, and leaves a hole in it. After that the second group of specialized cells comes and produces the new tissue that fills in the hole that was made by the first group.
W: Very good. This is a very complex process. In fact, the scientists who study human bones don't completely understand it yet. They are still trying to find out how it all actually works. Specifically, because sometimes after the first group of cells leaves a hole in the bone tissue, for some reason, the second group doesn't completely fill in the hole. And this can cause real problems. It can actually lead to a disease in which the bone becomes weak and is easily broken.
M: Ok, I get it. So if the scientists can figure out what makes the specialized ceils work, maybe they can find a way to make sure the second group of cells completely fills the hole in the bone tissue ever time. That'll prevent the disease from every occurring.
(23)
A．Two different types of bones in the human body.
B．How bones help the body move.
C．How bones continuously repair themselves.
D．The chemical composition of human bones.
第7题
What Is Death？
People in the past did not question the difference between life and death. They could see that a person died when his heart stopped beating. People have learned, however, that the body does not die immediately when the heart stops beating. They discovered that we remain alive as long as our brain remains active. Today the difference between life and death is not as easy to see as in the past. Modern medical devices can keep the heart beating and the lungs breathing long after the brain stops. But is this life？
This question has caused much debate among citizens in the United States. Many of them want a law that says a person is dead when the brain dies. A person should be considered dead when brain waves stop even if machines can keep the body alive. Such a law would permit doctors to speed removal (切除) of undiseased (没病的) organs for transplant (移植) operations.
The brain is made of thousands of millions of nerve cells. These cells send and receive millions of chemical and electrical messages every day. In this way the brain controls the other body activities. Nerve-cell experts say it is usually easy to tell when the brain has died. They put small electrodes (电极) on a person's skull (头骨) to measure the electrical signals that pass in and out of the brain. These brain waves are recorded on a television screen or on paper. The waves move up and down every time the brain receives messages from the nerve cells. The brain is dead when the waves stop moving.
Although there are people who oppose the idea of a law on brain block for various reasons, the idea of brain wave activity as a test of death is slowly being accepted.
第 31 题 People in the past held that the difference between life and death
A．did not exist.
B．was easy to tell.
C．lay in the brain.
D．was open to debate.
