相关考题
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未知题型
指出下列连续型随机变量分布( )。
A.二项分布
B．正态分布
C．均匀分布
D．泊松分布
E．指数分布 -
单项选择题
根据下列文章,请回答 23～30 题。 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. 第 23 题 Paragraph 2________A．Early Ideas about the Sky and the StarsB．The Importance of the Sun to Life on EarthC．Primitive Knowledge of the Moon D．The Sun in Autumn and Winter E．Early Ideas about the EarthF．Collecting Evidence about the Sun
A.
2
B.
3
C.
4
D.
5
E.Early
F.The
G.Primitive
H.The
I.Early
J.Collecting -
单项选择题
根据下列文章,请回答 36～40 题。 A Thirsty World The world is not only hungry, it is also thirsty for water. This may seem strange to you, since nearly 75% of the earth's surface is covered with water. But about 97% of this huge amount is sea-water, or salt water. Man can only drink and use the other 3% - the fresh water that comes from rivers, lakes, underground, and other sources. And we cannot even use all of that, because some of it is in the form. of icebergs (冰山) and glaciers (冰山). Even worse, some of it has been polluted.At the moment, this small amount of fresh water is still enough for us. However, our need for water is increasing rapidly. Only if we take steps to deal with this problem now can we avoid a severe worldwide water shortage later on. A limited water supply would have a bad effect on agriculture and industry.In addition to stopping wasting our precious water, one useful step we should take is to develop ways of reusing it. Experiments have already been done in this field, but only on a small scale.Today, in most large cities, water is used only once and it eventually returns to the sea or runs into underground storage tanks. But it is possible to pipe water that has been used to a purifying (净化) plant. There it can be filtered (过滤) and treated with chemicals so that it can be used again just as if it were fresh from a spring.But even if every large city purified and reused its water, we still would not have enough. Where could we turn next? To the oceans! All we'd have to do to make use of the vast amount of sea-water is - remove the salt. This salt-removing process is already, in use in many parts of the world.So if we take all these steps, we'll be in no danger of drying up! 第 36 题 The phrase 'the world' in the first line of the passage refers toA．'man'.B．'you'.C．'woman'.D．'they'.
A.
At
B.
In
C.
Today,
D.
But
E.
So
F.'man'.
B．'you'.
C．'woman'.
D．'they'.
