填空题In astrology, the earth is regarded as the center of the solar system.____

共用题干
Earth's Inner Core

Scientists have long struggled to understand what lies at the planet's center.Direct
observation of its center is impossible,so researchers must_________(1)to other evidence.
In 1889,a German scientist detected a severe earthquake in Japan.Geophysicists
concluded that shock waves_________(2) jolts（晃动）from one side of Earth through
the center to the other side.Then in 1936,Danish geophysicist lnge Lehmann studied the
waves' __________ (3) to determine that within Earth's core of molten（熔化了的）iron
lies a solid inner core一but_________(4) that core was made of eluded（难倒）her.
Other geophysicists quickly determined that Lehmann's inner core was composed mostly
_________(5) iron.Since then,Lehmann's discovery has _________(6)
conventional Earth science.
But now scientists are challenging traditional theory with new and radical_________
(7).For example,Earth's center could actually contain an"inner core within the inner
core."claim lshii and colleague Adam Dziewonski.
Analyzing hundreds of thousands of earthquake wave _________(8),they
maintain that the inner core has at its heart a tiny, even more solid sphere（球体）.This
sphere"may be the oldest fossil_________(9)from the formation of Earth,"says Dziewonski.
Dziewonski and Ishii speculate that shortly _________(10)Earth formed around
4.8 billion years ago,a giant asteroid（小行星）smashed into the young planet and nearly
melted it.But Earth's center didn't quite melt;it_________(11)mass as the planet
cooled. The core within a core may be the kernel（核心）that endured. " Its presence
could change our basic ideas about the_________(12)of the planet,"Dziewonski
says.
Dziewonski's idea is tame（温和的）compared to the_________( 13 ) theories of
independent geophysicist J. Marvin Herndon.Earth's inner core is made not of iron,he
claims,but a_________(14)of nickel and silicon.Herndon has a truly revolutionary
notion : Within the nickel silicide（硅化物）inner core is also an "inner" inner core一an
8km-wide ball of the element uranium.Uranium is radioactive.Herndon thinks the uranium
releases heat energy as its atoms_________(15)fission-split and crash into one
another in a chain reaction.In other words,we may live on top of a gigantic, "natural"
nuclear power plant.

_________(1)
A:try
B:leave
C:turn
D:point

共用题干
Early Ideas about the Universe

1 Early man got his ideas about the universe by looking at the stars as you do.He
observed carefully,and learned many things about the sun,the moon,and the stars.
2 Suppose you were asked to collect evidence about the sun as early man did.You might
go out morning after morning and see it come up in the east.Even on cloudy mornings,you
would observe that the darkness goes away and the world becomes light.You might not see
the sun but would be sure it is there,because you notice that the earth warms up.As you
continued,the sun climbs higher in the sky each day during part of the year. It stays in the
sky longer. The earth gets warmer. Things begin to grow. It is spring and then summer.
3 After a while the sun stays in the sky for shorter and shorter periods.Many plants begin
to die.Leaves fall.Winter comes.Year after year this is repeated and you cannot tell
exactly why it happens.But you realize that the sun seems to make the difference.
Primitive（原始的）man felt that since the sun was so powerful it must be a god. It may
seem silly to us now to worship（崇拜）a sun-god, but primitive man was right about the
importance of the sun to life on earth.
4 You have been told that the world is round.But suppose no one had ever taught you
that the world was like a huge ball.Would you have ever thought of it yourself?You cannot
see the curve（曲线）of the earth at once. You would have no idea of how big it was.
That's why early man believed that the earth was small and flat.Such ideas appeared from
the evidence they had.
5 If you watch the stars night after night,you will see them rise and set.As you look at
the sky,it is not difficult to imagine that you are in the center of a vast collection of twinkling
（闪烁）lights. Some early astronomers（天文学家）believed the sky was a crystal shell or
series of crystal shells,one inside the other. They believed this because that is what the
night sky looked like.For many centuries,men believed that the earth was the center of
the universe and that the sun,the moon,and the stars circled around it.

Early man thought the earth was the center of the universe because_________.
A:he did not observe the sun carefully enough
B:he could not see its curve
C:the sun,the moon and the stars seemed to move around it
D:the earth circles around the sun
E:it looked like that at night
F:it has power over life on earth

共用题干
Weight on and off the Earth We are so used to.our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted.Because we can feel that things are heavy,we think of "weight"as being a fixed quality in an object,but it is not really fixed at all.If you could take a one-pound packet of butter 4,000 miles out from the earth,it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space?The reason is this:all objects have a natural attraction for all other objects;this is called gravitational attraction.But this power of attraction between two obects gets weaker as they get farther apart.When the butter was at the surface of the earth,it was 4,000 miles from the center.When we took the butter 4,000 miles out,it was 8,000 miles from the center,which is twice the distance.If you double the distance between two objects,their gravitational attraction decreases two times two.If you treble the distance, it gets nine times weaker(three times three)and so on. So this is one of the first things we need to remember that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon?At the distance the puii of the earth is about 4,000 times smaller than it is here on the surface,so we can forget all about the earth-pull on our butter. On the other hand,on the moon there will be an attraction between the butter and the moon,but the butter will weigh only about one-sixth as much as it does on the earth.This is because the moon is so much smaller than the earth.The amount of gravitational pull that a body produces depends on the amount of material in it.A packet of butter has a gravitational pull of its own;but this is very small in relation to the pull of something as large as the moon,or the earth,or the sun.

We find it hard to break free from ideas connected with living on the earth because______.
A:it demands too great an effort for us to do so
B:we are too familiar with the way things are to question the ideas
C:we have proved that those ideas are correct
D:we are so sure of ourselves that we never doubt anything on the earth

共用题干
Weight on and off the Earth We are so used to.our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted.Because we can feel that things are heavy,we think of "weight"as being a fixed quality in an object,but it is not really fixed at all.If you could take a one-pound packet of butter 4,000 miles out from the earth,it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space?The reason is this:all objects have a natural attraction for all other objects;this is called gravitational attraction.But this power of attraction between two obects gets weaker as they get farther apart.When the butter was at the surface of the earth,it was 4,000 miles from the center.When we took the butter 4,000 miles out,it was 8,000 miles from the center,which is twice the distance.If you double the distance between two objects,their gravitational attraction decreases two times two.If you treble the distance, it gets nine times weaker(three times three)and so on. So this is one of the first things we need to remember that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon?At the distance the puii of the earth is about 4,000 times smaller than it is here on the surface,so we can forget all about the earth-pull on our butter. On the other hand,on the moon there will be an attraction between the butter and the moon,but the butter will weigh only about one-sixth as much as it does on the earth.This is because the moon is so much smaller than the earth.The amount of gravitational pull that a body produces depends on the amount of material in it.A packet of butter has a gravitational pull of its own;but this is very small in relation to the pull of something as large as the moon,or the earth,or the sun.

According to the passage,"weight"should be understood in the sense that
A:it is fixed if it is outside the earth's gravitational puli
B:it decreases four times when it is 4,000 miles from the earth's center
C:it varies with the change of the gravitational attraction between two objects
D:things increase in amount as they are closer to the earth's surface

共用题干
Weight on and off the Earth We are so used to.our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted.Because we can feel that things are heavy,we think of "weight"as being a fixed quality in an object,but it is not really fixed at all.If you could take a one-pound packet of butter 4,000 miles out from the earth,it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space?The reason is this:all objects have a natural attraction for all other objects;this is called gravitational attraction.But this power of attraction between two obects gets weaker as they get farther apart.When the butter was at the surface of the earth,it was 4,000 miles from the center.When we took the butter 4,000 miles out,it was 8,000 miles from the center,which is twice the distance.If you double the distance between two objects,their gravitational attraction decreases two times two.If you treble the distance, it gets nine times weaker(three times three)and so on. So this is one of the first things we need to remember that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon?At the distance the puii of the earth is about 4,000 times smaller than it is here on the surface,so we can forget all about the earth-pull on our butter. On the other hand,on the moon there will be an attraction between the butter and the moon,but the butter will weigh only about one-sixth as much as it does on the earth.This is because the moon is so much smaller than the earth.The amount of gravitational pull that a body produces depends on the amount of material in it.A packet of butter has a gravitational pull of its own;but this is very small in relation to the pull of something as large as the moon,or the earth,or the sun.

How much would four pounds of tea weigh if it was taken 4,000 miles out from the surface of the earth?
A:1 pound.
B:2 pounds.
C:3 pounds.
D:4 pounds.