Night of the Living Ants When an ant dies,other ants move th..

第1题

Night of the Living Ants When an ant dies,other ants move the dead insect out of the nest.

Night of the Living Ants

When an ant dies，other ants move the dead insect out of the nest．This behavior. is interesting to scientists，who wonder how ants know for sure-and so soon-that another ant is dead．

Dong-Hwan Choe，a scientist at the University of California，found that Argentine ants have a chemical on the outside of their bodies that signals to other ants，“I’m dead-take me away．”

But there's a twist to Choe's discovery．Choe says that the living ants-not just the dead ones -have this death chemical．In other words，while an ant crawls around，perhaps in a picnic or home，it's telling other ants that it's dead．

What keeps ants from hauling away the living dead?Choe found that Argentine ants have two additional chemicals on their bodies，and these tell nearby ants something like，“Wait-I'm not dead yet．” So Choe's research turned up two sets of chemical signals in ants：one says，“I'm dead，”the other set says，“I'm not dead yet．”

Other scientists have tried to figure out how ants know when another ant is dead．If an ant is knocked unconscious，other ants leave it alone until it wakes up．That means ants know that unmoving ants can still be alive．

Choe suspects that when an Argentine ant dies．the chemical that says“Wait-I'm not dead yet” quickly goes away．Once that chemical is gone，only the one that says“I'm dead”is left．“It's because the dead ant no longer smells like a living ant that it gets carried to the graveyard(墓地)，not because its body releases new，unique chemicals after death，”said Choe．When other ants detect the“dead”chemical without the“not dead yet”chemical，they haul away the body．This was Choe's hypothesis(假设)．

To test his hypothesis，Choe and his team put different chemicals on Argentine ant pupae(蛹)． When the scientists used the“I'm dead”chemical，other ants quickly hauled the treated pupae away． When the scientists used the“Wait-I'm not dead yet”chemical，other ants left the treated pupae alone． Choe believes this behavior. shows that the“not dead yet”chemical overrides(优胜于)the“dead”chemical when picked up by adult ants．And that when an ant dies，the“not dead yet”chemical fades away． Other nearby ants then detect the remaining“dead”chemical and remove the body from the nest．

The phrase“this death chemical”in paragraph 3 refers to

A．the chemical that contains poison．

B．the chemical that announces death．

C．the chemical that prevents death．

D．the chemical that causes death．

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第2题

When evaluating the size of the deadweight loss due to a tax we know that the ( )

A、greater the elasticities of supply and demand, the greater the deadweight loss.

B、smaller the elasticities of supply and demand, the greater the deadweight loss.

C、greater the decrease in both quantity demanded and quantity supplied, the greater the deadweight loss.

D、primary factor that determines the size of the deadweight loss in the percentage tax is of price.

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第3题

Read the sentences and choose the correct ones. Brenda has just moved to a new school and has made a new friend, Paula. They are sitting in a snack bar after school talking. Paula asks Brenda," Tell me about your family." Brenda: "My family is a rather small one, with only three people, my father, my mother and me. My father is a doctor. My mother is a teacher. My mother is very patient and understanding while my father is not very patient. He is often quite loud and wants things to happen at once. We love each other very much. Although sometimes we might fight about things we feel strongly about, very soon we will change the subject and discuss something else. We're a happy family. How about you? Paula: "I have a big family with seven people, my grandparents, parents, two older brothers and me. We all live together in a big house. It is often very noisy in our house, especially at dinner time. Grandfather has a loud voice. But it is nice having my grandparents living with us. That means that when I come home from school there is always somebody there for me. We take care of one another, share housework, and often communicate all together. My brothers help me with problems I have with homework and I help them with problems they have with girls."

A、Brenda's father is patient.

B、Brenda is patient.

C、Brenda's mother is a patient.

D、Brenda's mother is patient.

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第4题

In the animal rights (), much is made of the volume of pain these animals () in the name of medical science. Activists deny that we are trying to help and say it is () of our evil and cruel (). A more reasonable argument, however, can be advanced in our (). Life is often () to animals and human beings. Teenagers are flung from trucks and suffer severe head (). Young children () able to walk find themselves at the bottom of swimming pools while a parent is occupied with something else. From everyday germs to gang (), no life is free of pain. Physicians hoping to relieve the eternal suffering of these tragedies have only three choices: 1) create an animal model of the problem to understand the process and test new therapies; 2) experiment on human beings (some experiments will succeed, most will fail); or 3) leave medical knowledge static, hoping that () discoveries will lead us forward.

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第5题

Learning Disabilities Learning disabilities are very common. They affect perhaps 10 perce

Learning Disabilities

Learning disabilities are very common. They affect perhaps 10 percent of all children. Four times as many boys as girls have learning disabilities.

Since about 1970, new research has helped brain scientists understand these problems better. Scientists now know there are many different kinds of learning disabilities and that they are caused by many different things. There is no longer any question that all learning disabilities result from differences in the way the train is organized.

You cannot look at a child and tell if he or she has a learning disability. There is no outward sign of the disorder. So some researchers began looking at the brain itself to learn what might be wrong.

In one study, researchers examined the brain of a learning-disabled person who had died in an accident. They found two unusual things. One involved cells in the left side of the brain, which control language. These cells normally are white. In the learning disabled person, however, these cells were gray. The researchers also found that many of the nerve cells were not in a line the way they should have been. The nerve cells were mixed together.

The study was carried out under the guidance of Norman Geschwind, an early expert on learning disabilities. Doctor Geschwind proposed that learning disabilities resulted mainly from problems in the left side of the brain. He velieved this side of the brain failed to develop normally. Probably, he said, nerve cells there did not conncts as they should. So the brain was like an electrical device in which the wires were crossed.

Other researchers did not examine brain tissue. Instead, they measured the brain’s electrical activity and made a map of the electrical signals.

Frank Dully experimented with this technique at Children’S Hospital Medical Centre in Boston. Doctor Dully found large differences in the brain activity of normal children and those with reading problems. The differences appeared throughout the brain. Doctor Duffy said his research is evidence that disabilities involve damage to a wide area of the brain, not just the left side.

第41题 Which of the following is NOT mentioned in the passage?____________.

A Learning disabilities may result from the unknown area of the train

B learning disabilities may result from damage to a wide area of the train

C Learning disabilities may result from abnormal organization of the train cells.

D Leaning disabilities may result from problems in the left side of the brain.

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第6题

Please Fasten Your Seatbelts Severe turbulence (湍流) can kill aircraft passengers. Now, in test flights over the Rocky Mountains, NASA (美国航空航天局) engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.

Clear-air turbulence often catches pilots by surprise. Invisible to radar, it is difficult to forecast and can hurl (用力抛出去) passengers about the cabin. In December 1997, one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 metres in a few seconds.

However, passengers can avoid serious injury by fastening their seatbelts. “It is the only antidote (对策) for this sort of things,” says Rod Bogue, project manager at NASA’s Dryden Flight Research Center in Edwards, California.

The centre’s new turbulence detector is based on lidar, or laser radar, Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect. The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air, the speed equals the plane’s airspeed. But as the particles swirl (打漩) in rough air, their speed of approach increases or decreases rapidly. The rate of change in speed corresponds to the severity (激烈程度) of the turbulence.

In a series of tests that began last month, a research jet flew repeatedly into disturbed air over the mountain ridges (山脉) near Pueblo, Colorado. The lidar detector spotted turbulence between 3 and 8 kilometres ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.

Bogue says that he had “ a comfortable amount of time” to fasten his seatbelt. The researchers are planning to improve the lidar’s range with a more powerful beam. The system could be installed on commercial aircraft in the next few years.

第6题：What does “clear-air turbulence” probably mean? （Paragraph 1）

A．A not very rough storm.

B．Unexpected disturbed air.

C．A kind of visible storm.

D．A storm over mountain ridges.

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