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

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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

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　　There are many problems connected with space travel．The first and greatest of them is gravity(重力)．If you let your pencil drop to the floor, you can see gravity in action．Everything is held to the earth by the force, which can be described by its weight．A rocket must go at least 2500 miles an hour to take anyone beyond the gravity of the earth into space．

　　Another problem is the strainthat a person feels when a rocket leaves the ground．Anything that is not moving tends to keep still．As the rocket leaves the ground, it pushes upwards strongly and the person in it is pushed back against the chair．Gravity gives the body a force equal to nine times its normal force．

　　Once out of the earth’s gravity, an astronaut is affected by another problem, weightlessness．Here, if a pencil drops, it does not fall．If a glass of water is turned upside down, the water will not fall out．All of us are used to gravity．Recent long flights have shown that the body needs special exercise in a spaceship．

(1)

The weight is ________ the force gravity gives the object．
[　　]
A．	different from
B．	morn than
C．	less than
D．	as much as

(2)

When a running car stops, the person in it is pushed ________．
[　　]
A．	forward
B．	upward
C．	backward
D．	downward

(3)

The passage mainly talks about ________．
[　　]
A．	space travel
B．	pleasure in spaceships
C．	problems in space travel
D．	gravity of the earth

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.

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

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

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.

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

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

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.

“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.

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.

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

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

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.

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

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

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