Listening and Note-taking
Sleep
It’s clear that everyone needs to sleep. Most people rarely think about how or why they sleep, however. We know that if we sleep well we feel rested. If we don’t sleep enough, we often feel tired and irritable. It ems that there are two purpos of sleep: physical rest and emotional or psychological rest. We need to rest our bodies and our minds. Both are important in order for us to be healthy.
Each night we alternate between two kinds of sleep: active sleep and passive sleep. The passive sleep gives our body the rest that is needed and prepares us for active sleep in which dreaming occurs. And we are beginning to understand the importance of the dream stage in our sleep cycles.
Let’s look at the different kinds of sleep. They’re quite different. In passive sleep, the body is at rest. The heart slows down. The body process become very slow. We move very littl
跟我学e. And the brain becomes very inactive. This stage of sleep is known as slow-wave sleep becau the brain waves move in a very slow regular rhythm.
If a person continues to sleep, she or he enters a new stage, a more active stage. The body goes through veral changes: the brain temperature ris, the amount of blood in the brain increas, the body becomes very, very still, and the brain goes from being very inactive to being active. And as the brain becomes more active, the eyes begin to move rapidly. When the eyes begin to move, this is a sign of another change—the change is that the person is dreaming.
Throughout the night, people alternate between passive and active sleep. The brain rests, then it becomes active, then dreaming occurs. The cycle is repeated: the brain rests, then it becomes active, then dreaming occurs. This cycle is repeated veral times throughout the night. During eight hours of sleep people dream for a total of one and a half hours, on the average.
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All people experience the dream cycles. Many people say they don’t dream, or that the
y rarely dream. Doctors have studied the sleep cycle and have found that everyone dreams—in fact, that everyone needs to dream in order to stay healthy. It appears we need both kinds of sleep. We need passive sleep in order to rest our bodies. We need active sleep in order to dream. And dreaming helps us to rest our minds.
Passage 1 what is a black hole?
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外研版小学英语教案A black hole is a region of spacetime from which nothing can escape, even light. To e why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is traveling when it leaves you hand and the higher the ball will go before turning back. If you throw it hard enough it will never return; the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the escape velocity and for the earth is about 7miles a cond.
As a body is crushed into a smaller and smaller volume, the gravitational attraction increas, and hence the escape velocity gets bigger. Things have to be thrown harder and harder to escape. Eventually a point is reached when even light, which travels at 186
julie and juliahimationthousand miles a cond, is not traveling fast enough to escape. At this point, nothing can get out as nothing can travel faster than light. This is a black hole.
It is impossible to e a black hole directly becau no light can escape from them; they are black. But there are good reasons to think they exist.
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When a large star has been built all its fuel it explodes into a supernova. The stuff that is left collaps down to an extremely den object known as a neutron star. We know that the objects exist becau veral have been found using radio telescopes.
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If the neutron star is too large, the gravitational forces overwhelm the pressure gradients and collap cannot be halted. The neutron star continues to shrink until it finally becomes a black hole. This mass limit is only a couple of solar mass, that is about twice the mass of our sun, and so we should expect at least a few neutron stars to have this mass. Our sun is not particularly large; in fact it is quite small.
A supernova occurs in our galaxy once every 300 years, and in neighboring galaxies abo是否英文
ut 500 neutron stars have been identified. Therefore we are quite confident that there should also be some black holes.
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Passage 2 My Ancestor Was a Rhinoceros
At one time I thought my family was very different from every other family in the world. It happened becau I had trouble with a word. That word was ancestor. Today, I know what it means. An ancestor is someone, a man or woman, in your family. That person is now dead, and died many years, even hundreds of years, ago.
