The gravity on the earth is much that on the moon, do you know why? [ ]A. as strong as B. strong than C. so strong than D. stronger than 题目和参考答案——青夏教育精英家教网—

A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces (熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.

The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.

After the explosion gravity pulls in what’s left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so dense that a teaspoon of matter from it weighs billion of pounds.

The more the star shrinks, the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!

That’s what we know about black holes. What we don’t know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.

But if the black hole doesn’t keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world. They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a “white hole” in a different universe. As the black hole swallows light, the white hole shines brightly—somewhere else. But where? A different place, perhaps, or a different time — many years in the past or future.

Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed. So far the time being, black hole must remain a mystery.

Black holes are a mystery—but that hasn’t stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth’s energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste—a sort of huge waste disposal(处理) in the sky!

When the star begins to die ______.

A. there is no fuel left in it B. its outer layer goes into space first

C. a huge explosion will happen D. it doesn’t give off light any longer

Which of the following doesn’t help produce a black hole?

A. The gravity inside the star is very strong. B. The light can’t go out of the star.

C. The star becomes smaller and smaller D. The dying star shines very brightly.

The black hole ______.

A. continues becoming smaller and smaller all the time

B. goes into another universe and becomes a white hole

C. can pull in everything we know of in the world

D. will appear at another place at a different time

What’s the best title for this passage?

A. A New Scientific Discovery: Black Holes

B. How Do Black Holes Come Into Being?

C. What Are Black Holes?

D. Travel Through A Black Hole

Space travel is definitely bad for astronauts’ bones, reducing their bone density(密度) after only a month of weightlessness, according to French research published on Friday.

Laurence Vico and his fellow workers at St Etienne University called for more research into the effects of microgravity, after their study of 15 astronauts from the Russian MIR station showed bone loss continued throughout space flights.

“Bone loss was especially striking in four astronauts, ” the scientists reported in the Lancet Medical Journal.

They measured the bone mineral density (BMD) of bones in the forearm(前臂) and lower leg of the astronauts who had spent one to six months in space.

The BMD loss was significant in the tibia(胫骨) of the lower leg, a weight-bearing bone, but barely changed in the radius(桡骨) of the forearm. “Our results indicate the need to investigate not only different bones, but also different areas of the same bone since not all sites of the skeleton (骨架) are similarly affected by space conditions, ” they added.

Without gravity the body isn’t bearing any weight so there is no need for calcium (钙) which makes bones strong, and it becomes empty into the bloodstream.

The research team suggested in future scientists should try to determine if the loss of bone density was only on weight-bearing bones on longer flights, also the possible recovery after returning to Earth.

1. French scientists did their research on Russian astronauts, because _______.

A. they only cared for the Russian astronauts

B. they were not interested in their own astronauts

C. the Russian government invited them to do their research

D. the Russian astronauts worked in space for a long time

2. Scientists have found that _______.

A. the BMD loss may cause serious illness to astronauts

B. the BMD loss may cause some change in astronauts’ bodies

C. astronauts shouldn’t care about the BMD loss

D. astronauts should take some calcium before space travel

3. What cause the BMD loss to astronauts, according to this passage?

A. The food they eat in space. B. The drinks they take in space.

C. The temperature in space. D. The gravity in space.

4. In the third paragraph, the word “striking” means ______.

A. unusual B. simple C. weak D. slow

A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces(熔炉) that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.

The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.

After the explosion gravity pulls in what’s left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so dense that a teaspoon of matter from it weighs billion of pounds.

The more the star shrinks, the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is unbelievably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!

That’s what we know about black holes. What we don’t know is this: What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.

But if the black hole doesn’t keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world．They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a “white hole” in a different universe. As the black hole swallows light, the white hole shines brightly — somewhere else. But where? A different place, perhaps, or a different time — many years in the past or future.

Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed．So far the time being, black hole must remain a mystery.

Black holes are a mystery—but that hasn’t stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth’s energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste—a sort of huge waste disposal (处理) in the sky!

When the star begins to die ______.

A．there is no fuel left in it B．its outer layer goes into space first

C．a huge explosion will happen D．it doesn’t give off light any longer

Which of the following doesn’t help produce a black hole?

A．The gravity inside the star is very strong.

B．The light can’t go out of the star.

C．The star becomes smaller and smaller

D．The dying star shines very brightly.

The black hole ______.

A．continues becoming smaller and smaller all the time

B．goes into another universe and becomes a white hole

C．can pull in everything we know of in the world

D．will appear at another place at a different time

The author mainly intended to tell us _____.

A．A New Scientific Discovery: Black Holes

B．How Black Holes Came Into Being

C．What Black Holes Are

D．Travel Through A Black Hole

Sixty-five million years ago, an asteroid (小行星) that crashed on Earth led to the disappearance of the largest animals that have ever walked our planet – the dinosaurs. At least, this is what some scientists believe. But that accident happened so long ago. People have come to believe that we are free of threats from asteroids and everything else from space.

However, what happened on Feb 15 , 2013 was a reminder that we’re just as vulnerable as the dinosaurs once were. Two objects from space – a meteor (陨石) and an asteroid called 2012 DA14 – visited Earth’s atmosphere on the same day. The former fell in Russia, injuring 1,200 people, while the latter passed by Earth at a record-setting close distance.

Scientists had been expecting the asteroid since last year, but the meteor was a surprise. NASA’s telescope system only detects asteroids at least 50 meters in diameter (直径), which is just about the size of 2012 DA14. But the meteor was much smaller, which made it harder to spot.

But what if we do spot an asteroid that is headed right for Earth? There are several possible ways in which dangerous asteroids could be made to change its orbit. Which method is best depends on several factors and most importantly – how much time we have to stop it.

If there is enough time before the hit, we can send off a heavy spacecraft to travel alongside the asteroid. The gravity from the spacecraft would gradually change the rock’s orbit. Besides that, scientists could one day use sun-powered lasers to either make asteroids disappear or change their course. If there’s not enough time, we’ll have to go after the asteroid with a spacecraft and change its orbit with a crash. Finally, if things are truly desperate, there will be only one choice left – to use a nuclear bomb. That could turn the asteroid into a meteor shower, which would be even more dangerous.

1.The author mentioned the asteroid that led to the dinosaurs’ dying out to ______.

A. show that asteroids fall from space frequently

B. alert people about the possible danger of objects falling from space

C. inform readers about the constant threats the Earth faces

D. suggest that there are still many mysteries about the universe

2.The underlined word “vulnerable” in the second paragraph probably means ______.

A. unprotected B. lonely C. stupid D. self-important

3.Which of the following statements is TRUE about the meteor that fell to the Earth in Russia?

A. It passed by the Earth at a close distance.

B. It was spotted by NASA’s telescope system a year ago.

C. It is about the same size as the asteroid that passed by the Earth.

D. It fell to the Earth and caused great damage to the local community.

4.What is the main idea of the article?

A. Learning about asteroids and meteors.

B. The threats of objects from space and possible solutions.

C. NASA’s latest technology to discover visitors to the Earth from space.

D. How to measure the damage of collisions from asteroids and meteors.

Have you ever wondered?

1.Why do airplanes take longer to fly west than east?

It can take five hours to go west-east from New York(NY) to London but seven hours to travel east-west from London to NY. The reason for the difference is an atmospheric phenomenon know as the jet(喷射) stream. The jet stream is a very high altitude wind which always blows from the west to the east across the Atlantic. The planes movement a constams air speed thus go faster in the west-east direction when the air moving with the wind than in the opposite direction.

2 What would happen if the gravity on Earth was suddenly turned off?

Supposing we could magically turn off gravity. Would buildings and other structures float away? What happened would depend on how strongly the things were attached to the Earth. The Earth is moving at quite a speed moving at over a thousand miles per hour. If you turn something round your head on a string, it goes around in a circle until you let go of the strong go of the string. Things not attacked to the Earth would fly off in a straight line . People in buildings would suddenly shoot upwards at a great speed until they hit the ceiling. Most things would fly off into space.

1.What information coa we get from the first passage?

A.tis the iet stoomn that affeets how fast airplanes fly.

B.Planes go slower when they are moving with the wind.

C.It takes more time to fly from NY to London than from London to NY.

D.The jet stream always blows from the east to the west across the Atantic.

2.The word“shoot”underlined in the 2nd passage probably means“__________”.

A.send for

B.move quickly

C.come out

D.grow quickly

3.It can be interred that without gravity_________.

A.buildings and other structures would float away

B.trees and buildings would not so easily fly off

C.something around your head would not float away

D.everything outside buildings would fly off into space

4.Where can wemost probably read this text?

A.In s research paper

B.In a tort story.

C.In a travel magazine.

D.In a student’s book.

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