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What do scientists think causes dreams？
A．Sleep.
B．Scientists have not found the reason up to now.
C．REM sleep.
D．It is not mentioned in the article, but scientists have known it.
答案
更多“What do scientists think causes dreams？ A．Sleep.B．Scientists have not found th”相关的问题
第1题
What do we learn about scientists in earlier times？
A．They claimed to know nothing about nature.
B．They believed in results from scientific observation.
C．They paid much attention to the problems they didn't understand.
D．They invented false theories to explain things they didn't understand.
第2题
Land is becoming desert little by little because ______.
A．plants can't grow there
B．there is not enough rain
C．people haven't done what scientists wish them to do
D．scientists know little about the deserts
第3题
听力原文： Why don't birds got lost on their long migratory flights？ Scientists have puzzled over this question for many years. Now they're beginning to fill in the blanks.
Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly mainly by night？ Tests with artificial stars have proved conclusively that certain night-flying birds are able to follow the stars in their long-distance flights.
One such bird—a warbler—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 at migration time. The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the make-believe stars caused a change in the direction of his flight.
Scientists think that warblers, when flying in daylight, use the sun for guidance. But the stars are apparently their principal means of navigation. What do they do when the stars are hidden by clouds？ Apparently, they find their way by such landmarks as mountain ranges, coast lines, and rivet courses. But when it's too dark to see these, the warblers circle helplessly, unable to get their bearings.
(33)
A．Birds have to be taught to navigate.
B．A bird that has been caged will not.
C．Some birds cannot fly at night.
D．Some birds seem instinctively to follow the stars when flying at night.
第4题
听力原文：M: Hi, Jane! Did you watch that documentary on TV last night？
W: No, I was in a meeting, and didn't get home until 11:50. What was it about'？
M: It was about insects.
W: Insects？
M: Yeah! Do you know they are the most successful creatures on the planet？
W: What, more successful than humans？
M: Well, think about it! They were around long before people were--there are far more insects than humans--I mean, trillions of them! And they are reproducing all the time!
W: Well, I suppose that's true!
M: And they are incredibly adaptable.
W: In what way？
M: Well, take mosquitoes for example. You know, they spread malaria. Malaria is still a big problem in the world. The trouble is that every time we try to wipe out the mosquitoes with some new insecticide, they change their body-chemistry!
W: Haven't the scientists just brought out a new insecticide to fight mosquitoes？
M: Yes, they have. But I bet that within five years the mosquitoes will simply adapt again!
W: I suppose it keeps the scientists employed!
M: Yes! You know, I'd really like to work in that field after I graduate.
W: Why not!
(20)
A．Only mosquitoes can change their body-chemistry.
B．They can transmit a serious disease.
C．We can wipe them out with new insecticide.
D．Within five years scientists will have found a way to kill them all.
第7题
What can scientists do now？ 查看材料
A.Prescreen a baby"s sex.
B.Screen babies for desirable attributes.
C.Insert genes that parents want.
D.Craft genes in a lab.
第8题
At the beginning of this century, almost everybody believed in work. But by the end of this century, e might be thinking quite differently. Today, people are divided into social classes in accordance with the types of work they do; tomorrow, t is more than likely we will be divided according to the types of games we play.
This change in the use of our time may give rise to a now profession called" fun specialists," who will fill the same functions as our current career specialists. They will show us how to get the most fun and enjoyment out of our leisure time. Someday people will no longer be known primarily by the work they do.
What do scientists tell us about jobs in foreseeable future？
A．Most people will do hi-tech jobs.
B．People will work with more computers.
C．Very few people will have to work.
D．No people will be working at all.
第9题
Where Have All the Bees Gone？
Scientists who study insects have a real mystery on their hands．A11 across the country，honeybees are leaving their hives and never returning. Researcher call this phenomenon colony—collapse1 disorder．According to surveys of beekeepers across the country，25 to 4o percent of the honeybees in the United States have vanished from their hives since last fall .So far，no one can explain why．
Colony collapse is a serious concern because bees play an important 11ole in the production of about one—third of the foods we eat．As they feed，honeybees spread pollen from flower to flower．Without this process，a plant can’t produce seeds or fruits．
NOW，a group of scientists and beekeepers have teamed up to try to figure out what’s causing the alarming collapse of so many colonies． By sharing their expertise in honeybee behavior，health， and nutrition，team members hope to and out what’s contributing to the decline and to prevent bee disappearances in the future．
It could be that disease is causing the disappearance of the bees．To explore that possibility，Jay Evans，a researcher at the United States Department of Agriculture（USDA）Bee Research Laboratory2，examines bees taken from colonies that are collapsing． “We know what s healthy bee should look like on the inside，and we can look for physical signs of disease，”he says．And bees from collapsing
colonies don’t look very healthy． “Their stomachs arc：worn down，compared to the stomachs of healthy bees，”Evan8 says．It may be that a parasite is damaging the bees’ digestive organs．Their immune systems may not be working as they should．Moreover，they have high levels of bacteria inside their bodies．
Another cause of colony—collapse disorder may be certain chemicals that farmers apply to kill unwanted insects on crops，says Jerry Hayes，chief bee inspector for the Florida Department of Agricuhure3．Some studies，he says，suggest that a certain type of insecticide affects the honeybee’s
nervous system（which includes the brain）and memory．“It seems like honeybees are going out and getting confused about where to go and what to do，”he says.
If it turns out that a disease is contributing to colony collapse，bees’ genes could explain why some colonies have collapsed and others have not．In any group of bees there are many different kinds of genes．The more different genes a group has，the higher the group’s genetic diversity.So far scientists haven，t determined the role of genetic diversity in colony collapse，but it’s a promising theory，says Evans．
第 36 题 What is the mystery that researchers find hard to explain？
A．Honeybees are flying all across the country.
B．25-40 percent of the honeybees in the US have died.
C．Honeybees are leaving their hives and do not return.
D．Honeybee hives are in disorder．
第10题
Where Have All the Bees Gone？
Scientists who study insects have a real mystery on their hands. All across the country, honeybees are leaving their hives and never returning. Researchers call this phenomenon colony-collapse (瓦解) disorder. According to surveys of beekeepers (养蜂人) across the country, 25 to 40 percent of the honeybees in the United States have vanished from their hives (麻疹) since last fall. So far, no one can explain why.
Colony collapse is a serious concern because bees play an important role in the production of about one-third of the foods we eat. As they feed, honeybees spread pollen from flower to flower. Without this process, a plant can't produce seeds or fruits. Now, a group of scientists and beekeepers have teamed up to try to figure out what's causing the alarming collapse of so many colonies. By sharing their expertise (专家的意见) in honeybee behavior, health, and nutrition, team members hope to find out what's contributing to the decline and to prevent bee disappearances in the future.
It could be that disease is causing the disappearance of the bees. To explore that possibility, Jay Evans, a researcher at the United States Department of Agriculture (USDA) Bee Research Laboratory, examines bees taken from colonies that are collapsing. "We know what s healthy bee should look like on the inside, and we can look for physical signs of disease," he says. And bees from collapsing colonies don't look very healthy. "Their stomachs are worn down, compared to the stomachs of healthy bees," Evans says. It may be that a parasite is damaging the bees' digestive organs. Their immune systems may not be working as they should. Moreover, they have high levels of bacteria inside their bodies.
Another cause of colony-collapse disorder may be certain chemicals that farmers apply to kill unwanted insects on crops, says Jerry Hayes, chief bee inspector for the Florida Department of Agriculture. Some studies, he says, suggest that a certain type of insecticide affects the honeybee's nervous system (which includes the brain) and memory. "It seems like honeybees are going out and getting confused about where to go and what to do," he says.
If it turns out that a disease is contributing to colony collapse, bees' genes could explain why some colonies have collapsed and others have not. In any group of bees there are many different kinds of genes. The more different genes a group has, the higher the group's genetic diversity. So far scientists haven't determined the role of genetic diversity (差异) in colony collapse, but it's a promising theory, says Evans.
What is the mystery that researchers find hard to explain？
A．Honeybees are flying all across the country.
B．25--40 percent of the honeybees in the US have died.
C．Honeybees are leaving their hives and do not return.
D．Honeybee hives are in disorder.
