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Scientists counted the number of stars________.
A．to illustrate the impact of light pollution
B．to compare air quality in different areas
C．to see how the sky has changed with time
D．to arouse public interest in space
答案
更多“Scientists counted the number of stars________.A．to illustrate the impact of light polluti”相关的问题
第1题
Radiocarbon Dating
Nowadays scientists can answer many questions about the past through a technique called radiocarbon(放射性碳), or carbon-14, dating. One key to understanding how and why something happened is to discover when it happened.
Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at the University of Chicago. An atom of ordinary carbon, called carbon-12, has six protons(质子) and six neutrons(中子) in its nucleus. Carbon-14, or C-14, is a radioactive, unstable form. of carbon that has two extra neutrons(原子核). It returns to a more stable form. of carbon through a process called decay(衰减). This process involves the loss of the extra neutrons and energy from the nucleus.
In Libby's radiocarbon dating technique, the weak radioactive emissions(放射) from this decay process are counted by instruments such as a radiation detector and counter. The decay rate is used to determine the proportion of C-14 atoms in the sample being dated.
Carbon-14 is produced in the Earth's atmosphere when nitrogen(氮)-14, or N-14, interacts with cosmic rays(宇宙射线). Scientists believe since the Earth was formed, the amount of nitrogen in the atmosphere has remained constant. Consequently, C-14 formation is thought to occur at a constant rate. Now ratio of C-14 to other carbon atoms in the atmosphere is known. Most scientists agree that this ratio is useful for dating items back to at least 50,000 years.
All life on Earth is made of organic molecules(分子) that contain carbon atoms coming from the atmosphere. So all living things have about the same ratio of C-14 atoms to other carbon atoms in their tissues(组织). Once an organism(有机体) dies it stops taking in carbon in any form, and the C-14 already present begins to decay. Over time the amount of C-14 in the material decreases, and the ratio of C-14 to other carbon atoms goes down. In terms of radiocarbon dating, the fewer C-14 atoms in a sample, the older that sample is.
Nowadays many scientists depend on radiocarbon for dating age-old objects.
A．Right
B．Wrong
C．Not mentioned
第2题
A.balanced
B.counted
C.weighed
D.applied
第3题
A.if
B.whether
C.that
D.as
第4题
"What's wrong with you?" asked Mr.South.
"Nothing,Mr.South," said the man,"But…"
The man began to smile and said,"Don't you（）me,Mr.South? You cured (治愈) my rheumatism(风湿病) three years ago."
"Mr.Bell?"
"Yes.Did you（）me not to get myself wet?"
"Yes,I did," answered the doctor.
"Well.I come here to ask you if you think it's OK for me to take a bath now?"
A.clock B.buy C.tell D.about E.remember
第5题
experimenting on mice. They are studying the relationship between diet and health. At this time, over one hundred experiments are being done in this laboratory.
In one of these experiments, the scientists are studying the relationship between the amount of food the mice eat and their health. The mice are in three groups. All three groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating one cup of food each day, the second group is eating two cups, and the third group of mice is eating three cups.
After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Most of the day, they are running, playing with one another, and using the equipment in their cages. Also, they are living longer. Mice usually live for two years. Most of the mice in this group are still alive after three years.
The second group of mice is normal weight. They are healthy, too. They are active, but not as active as the thinner mice. But they are only living about two years, not the three years or more of the thinner mice.
The last group of mice is receiving more food than the other two groups. Most of the day, these mice are eating or sleeping. They are not very active. These mice are living longer than the scientists thought - about a year and a half. But they aren't as healthy. They're sick more often than the other two groups.
(1)、The scientists in the laboratory are studying the relationship between the amount of food and diet.
A：T
B：F
(2)、The first two groups are receiving the most food.
A：T
B：F
(3)、The first group is the thinnest because they do not have a healthy diet.
A：T
B：F
(4)、Normal mice usually live for two years.
A：T
B：F
(5)、The text tells us that people who eat less and exercise more will live longer.
A：T
B：F
第6题
Of course, scientists can't answer all of your questions. If we ask, "Why is the ocean full of salty" scientists will say that the salt comes from rocks. When a rock gets very hot or very cold, it cracks. Rain falls into the cracks. The rain then carries the salt into he earth and into the rivers. The rivers carry the salt into the ocean. But then we ask, "What happens to the salt in the ocean？ The ocean doesn't get more slat every year". Scientists are not sure about the answer to this question.
We know a lot about our world. But there are still many answers that we do not have, and we are curious.
The main idea of this passage is ______.
A．people feel cool when they are near a lake or river
B．scientists can explain everything we want to know
C．scientists can explain many things but not everything
D．the salt in the ocean comes from rocks
第7题
Not long age, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by night？ Tests with artificial stars have proved that certain night - flying birds are able to follow the stars in their long - distance flights.
A dove (鸽子) had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird's cage was placed under an artificial star - filled sky. (76) The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the artificial stars caused a change in the direction of his flight.
(77) But the stars are apparently their principal means of navigation (航行) only. When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it's too dark to see these, the doves circle helplessly, unable to find their way.
The reason why birds don't get lost on long flights ______.
A．have been known to scientists for many years
B．have only recently been discovered
C．are known by us
D．will probably remain a mystery
第8题
Life on Mars
Perhaps more than anything else, scientists are eager to find out if Martian life existed in the past—or still exists.【61】telescopes first zoomed in【62】Mars in the 17th century, people have conjured up a wild【63】of images or what Martians might look like. But space probes like the 1997 Sojourner land rover have yielded no evidence of such alien beings.
Most experts agree that if life did at one time evolve on Mars, finding evidence of that life—which would likely take the form. of tiny organisms—won't be easy.【64】, many scientists are optimistic. "We've got organisms on Earth that adapted to life deep【65】the surface in underground water wells, " says Stephen Clifford. "【66】life like that evolved on Mars four billion years ago, there's no reason why it【67】today. "
【68】last year's disappointing losses, the future of Martian exploration looks【69】This year, two major
films about fictitious Mars missions—Red Planet and Missions to Mars—are certain to heighten interest in our planetary neighbour. More important, plans for new sets of NASA orbiters and landers—one to launch in 2001 , the other in 2003—are already in the works. Without a doubt, each new mission will inch scientists closer to【70】the mysteries of planet Mars.
(61)
A．When
B．Before
C．Ever since
D．Ever
第9题
The event happened in the early morning in one of the first days when Calvin Coolidge came into power. He and his family were living in the same third-floor suite at the Willard Hotel in Washington that they had moved in several years before. The former President's wife was still living in the White House.
Coolidge awoke to see a stranger go through his clothes, remove a wallet and a watch chain.
Coolidge spoke, "I wish you won't take that."
The thief, gaining his voice, said, "Why？"
"I don't mean the watch and chain, only the charm. Take it near the window and read what is on its back," the President said.
The thief read," Presented to Calvin Coolidge."
"Are you President Coolidge？" he asked.
The President answered "Yes, and the House of Representatives gave me that watch charm. I'm fond of it. It would do you no good. You want money. Let's talk this over."
Holding up the wallet, the young man said in a low voice, "I'll take this and leave everything else."
Coolidge, knowing there was $80 in it, persuaded the young man to sit down and talk. He told the President he and his college roommate had overspent during their holiday and did not have enough money to pay their hotel bill.
Coolidge added up the roommate and two rail tickets back to the college. Then he counted out $32 and said it was a loan.
He then told the young man "There is a guard in the corridor." The young man nodded and left through the same window as he had entered.
What caused the thief to meet the President？
A．He knew the President had lots of money.
B．He knew the President lived in the suite.
C．He wanted to be a rich businessman.
D．He wanted to steal some money.
第10题
For example, a grandmotherly woman staffing an animal rights booth at a recent street fair was distributing a brochure that encouraged readers not to use anything that comes from or is tested in animals — no meat, no fur, no medicines. Asked if she opposed immunizations, she wanted to know if vaccines come from animal research. When assured that they do, she replied, "Then I would have to say yes." Asked what will happen when epidemics return, she said, "Don't worry, scientists will find some way of using computers." Such well-meaning people just don't understand.
Scientists must communicate their message to the public in a compassionate, understandable way — in human terms, not in the language of molecular biology. We need to make clear the connection between animal research and a grandmother's hip replacement, a father's bypass operation, a baby's vaccinations, and even a pet's shots. To those who are unaware that animal research was needed to produce these treatments, as well as mew treatments and vaccines, animal research seems wasteful at best and cruel at worst.
Much can be done. Scientists could "adopt" middle school classes and present their own research. They should be quick to respond to letters to the editor, lest animal rights misinformation go unchallenged and ac- quire a deceptive appearance of truth. Research institutions could be opened to tours, to show that laboratory animals receive humane care. Finally, because the ultimate stakeholders are patients, the health research com- munity should actively recruit to its cause not only well-known personalities such as Stephen Cooper, who has made courageous statements about the value of animal research, but all who receive medical treatment. If good people do nothing, there is a real possibility that an uninformed citizenry Will extinguish the precious embers of medical progress.
The author begins his article with Edmund Burke's words to ______.
A．call on scientists to take some actions
B．criticize the misguided cause of animal rights
C．warn of the doom of biomedical research
D．show the triumph of the animal rights movement
