题目内容
Did you ever wonder why leaves change colors in autumn, or how it happens? Here’s a quick explanation.
First of all, you’ve probably noticed that not all trees lose their leaves. There are two major types of trees: deciduous trees and evergreens. Evergreens keep their leaves and stay green all year long. The deciduous trees are the ones that lose their leaves each year.
In autumn, the days begin to get shorter. The sun is also lower in the sky at noon, which causes temperatures to be cooler. The combination of less sunshine and lower temperatures is what causes the deciduous trees to drop their leaves. In winter, deciduous trees “go to sleep”, sort of like a bear goes into hibernation.
Leaves are the food factories for a plant. Unlike animals，plants make their own food by taking energy directly from the sun. Plants do this by using a chemical in their leaves called chlorophyll.
Chlorophyll is green. During the spring and summer the leaves of a deciduous tree look green because there is a lot of chlorophyll there. In autumn, however, the sunshine becomes more scarce and the leaves on the trees stop making new chlorophyll. As the old chlorophyll starts to break down, the green color of the leaf begins to go away.
You’ve probably also noticed that the leaves of different kinds of trees change different colors. The leaves of some trees turn yellow or orange, while the leaves of other trees turn bright red or purple. The different colors are caused by the different chemical reactions that are happening in the leaves.
For example, the leaves of some trees turn yellow when the chlorophyll breaks down. When the green chlorophyll goes away, a yellow pigment in the leaf becomes visible. The yellow pigment, called cartenoid, was already there during the summer, but is was not easily seen because there was too much green chlorophyll.
In other trees where the leaves turn red or purple a different chemical reaction takes place. In those leaves the chlorophyll also breaks down, but another chemical reaction takes place at the same time. Chemicals in the leaves, called starches, begin to change into chemicals called anthocyanins, which give the leaves their red and purple colors.
So next time you see the beautiful colors of autumn you will also know the science behind that beauty.
46. What is the correct term for trees that lose their leaves in the autumn?
A. Evergreens B. Deciduous C. Cartenoids D. Anthocyanins
47. Which of the following is NOT mentioned as a cause of trees dropping their leaves?
A. A change in temperature B. The amount of daylight available
C. Extra chlorophyll D. Chemical changes in the leaves
48. If there are 50 evergreens and 10 deciduous trees in a forest, in autumn what color are most of the leaves in the forest likely to be?
A. Green B. Red and purple
C. Yellow D. not enough information to determine the answer
49. Which of the following is only present in leaves during the autumn?
A. Chlorophyll B. Starch C. Cartenoids D. Anthocyanins
50. Where would such an article mostly likely be published?
A. In a book B. In a primary school science text book
C. In a magazine for young people D. All are equally likely
46-50 BCADC
解析
Did you ever look up at the moon and think you saw a man’s face there? When the moon is round and full, the shadows(影子) of the moon mountains and the lines of the moon valleys sometimes seem to show a giant nose and mouth and eyes. At least, some people think so.
If there were a man on the moon—instead of mountains and valleys that just look like the face of a man—what would he be like?
He would not be like anyone you know. He would not be like anyone anybody knows.
If the man on the moon were bothered by too much heat or cold the way Earth people are, he could not stay on the moon.
The moon becomes very, very hot. It becomes as hot as boiling water. And the moon becomes very, very cold. It becomes colder than ice.
Whatever part of the moon the sun shines on is hot and bright. The rest of the moon is cold and dark.
If the man on the moon had to breathe to stay alive, he couldn’t live on the moon because there’s no air there. He’d have to carry an oxygen tank, as astronauts do. There’s no food on the moon, either. Nothing grows—not even weeds（grass）.
If the man on the moon liked to climb mountains, he would be very happy. There are many high places there, such as the raised land around the holes, or craters(火山口), of the moon. Some of these rims are as tall as Earth’s highest mountains.
But if the man on the moon liked to swim, he would be unhappy. There is no water on the moon—just dust and rock.
When you think of what it’s like on the moon, you may wonder why it interests our scientists. One reason is that the moon is Earth’s nearest neighbor—it is the easiest place in space to get to.
Going back and forth between the moon and Earth, astronauts will get a lot of practice in space travel. Things learned on moon trips will be of great help to astronauts who later take long, long trips to some of the planets.
Scientists are also interested in the moon because it has no air. The air that surrounds Earth cuts down the view of the scientists who look at the stars through telescopes. A telescope on the moon would give them a clearer, closer view of the stars.（words: 411）
【小题1】What is the reason why our scientists are interested in the moon.?
| A．The moon is beautiful. |
| B．The moon is different from the earth. |
| C．The moon is Earth’s nearest neighbor—it is the easiest place in space to get to. |
| D．The moon is the easiest place in space to get to and it has no air, unlike Earth. |
| A．ball | B．hill | C．round edge | D．height |
| A．We can learn much from research on the Moon. |
| B．There may be human beings on the moon. |
| C．If there were a man on the Moon, there would be many similarities between the man on the Moon and on the Earth. |
| D．A telescope on the Moon would help scientists have a clearer, closer sight of the stars. |
Although English is not as old as Chinese , it is spoken by many people around the world every day. English speakers are always creating new words and we are often able to know where most words come from.
Sometimes, however, no one may really know where a word comes from. Did you ever think about why hamburgers are called hamburgers, especially when they are not made with ham? About a hundred years ago, some men went to America from Europe. They came from a big city in Germany called Hamburg. They didn’t speak good English, but they ate good food. When some Americans saw them eating round piece of beef, they asked the Germans what it was. The Germans didn’t understand the question and answered, “We come from Hamburg.” One of these Americans owned a restaurant, and had an idea. He cooked some round piece of bread and started selling them. Such bread came to be called “hamburgers”. Today, “hamburgers” are sold in many countries around the world.
Whether this story is true or not, it certainly is interesting. Knowing why any word has a certain meaning is interesting, too. This reason, for most English words, can be found in any large English dictionary.
【小题1】Hamburg is ____________
| A．a kind of food | B．a round piece of beef |
| C．the name of a village | D．a city in Germany |
| A．few Americans like hamburgers |
| B．hamburgers are made with beef |
| C．hamburgers are made with ham |
| D．hamburgers were first sold about a century ago |
| A．Where all the new words come from. |
| B．Where those Germans came from. |
| C．The reason why a word has a certain meaning. |
| D．The reason why English is spoken around the world. |
| A．China because it has a long history |
| B．English because Germans don’t speak good English |
| C．The round piece of beef which those people from Hamburg were eating |
| D．English speakers because they always create new words |