全新版大学英语听说教程第三册 Unit 06

Unit 6

Part B

Text 1

Why Do Leaves Change Color?

In some places, as days shorten and temperatures become crisp, the quiet green of summer foliage¹ is transformed into the vivid autumn of reds, oranges, yellows and browns before the leaves fall off the trees. In special years, the colors are truly breathtaking.

But have you ever wondered how and why this happens? To answer that question, we first have to understand what leaves are and what they do.

Leaves are Nature's food factories. Plants take water from the ground through their roots, and carbon dioxide from the air. Then they turn water and carbon dioxide into a kind of sugar, using sunlight and something called chlorophyll. This process is called photosynthesis². As chlorophyll is green, leaves are therefore also green in color.

During winter, there is not enough light or water to help plants produce sugar as their food for energy and as a building block for growing. The trees will rest, and live off the food they stored during the summer. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in summer, because they are covered up by the green chlorophyll.

The bright reds and purples we see in leaves are made mostly in fall. In some trees, like maples³, sugar, which is produced in the leaves during warm, sunny days, is kept from moving out of the leaves after photosynthesis stops. Sunlight and the cool nights of fall turn the sugar into a red color. The brown color of trees like oaks is made from wastes left in the leaves.

It is the combination of all these things that makes the beautiful colors we enjoy in fall.

Questions:

1. What is the passage mainly about?

2. Which of the following plays a major role in making leaves change color?

3. Why can't we see yellow and orange colours in leaves during summer?

4. Which of the following best describes the speaker's attitude toward his subject?

Text 2

Timing⁴ of Color Change in Trees

Many trees and shrubs⁵ change color in fall. For years, scientists have worked to understand the changes that happen to them. They find that three factors influence fall's colorful farewell -- leaf pigments⁶, length of night, and weather. The timing of the color change is mainly regulated by the increasing length of night. None of the other environmental influences, such as temperature, rainfall, food supply, are as unchanging as the steadily⁷ increasing length of night during fall. As days grow shorter, and nights grow longer and cooler, biochemical processes in leaves begin to paint the landscape with an explosion of colors. And Nature puts on one of its most spectacular displays of beauty.

The timing of the color change varies by species. Some species in southern forests can become vividly⁸ colorful in late summer while all other species are still vigorously green. Oaks put on their colors long after other species have already shed their leaves. These differences in timing among species seem to be genetically⁹ inherited, for a particular species, whether on a high mountain or in warmer lowlands, will change color at the same time.

However, some species are evergreens¹¹. Pines, for example, are green all the year round because they have toughened up. They have developed over the years a needle-like or scale-like foliage, which is covered with a heavy wax coating. And the liquid inside their cells contains cold-resistant elements. So the leaves of evergreens can safely withstand all but the most severe winter conditions, such as those in the Arctic.

Questions:

1. What does the speaker mainly tell us?

2. What are the two major kinds of trees that the speaker differentiates¹²?

3. By what is the timing of the color change mainly regulated?

4. Why do some species of trees remain evergreen¹⁰?

Part C

The Missing Monarchs¹⁴ (Part One)

The monarch¹³ butterfly has rich orange-gold wings outlined in black and decorated with small dots of white. It looks like a stained-glass window that has come alive as it flutters through the summer sunshine.

Across most of the United States and Canada monarchs take a long journey southward when the cold season sets in.

Monarchs from the western United States travel to a winter home on the California coast. But until recently, no one had ever seen the winter home of the eastern monarchs. For more than forty years, a Toronto-based Canadian zoologist¹⁵, Fred Urquhart, tried to solve the puzzling mystery of the missing monarch butterflies. His first step was to mark the butterflies. It took a long time to find a way to attach tags so the tag would stay in place and the butterfly could still fly. Many people volunteered to help. They caught, tagged, and set free again thousands of butterflies. Each tag bore a code to indicate the exact place where the butterfly had been tagged. A message also asked anyone who found the tagged butterfly to send the information to an address in Toronto, where it would reach the zoologist. Thus, the tags were to serve as the scientist's clues.

Their detective work paid off. Over the years they learned a great deal about the migration¹⁶ of the eastern monarch butterflies. These seemingly fragile creatures have been known to cover eighty miles in a single day! They can fly ten miles an hour, and some have been clocked at thirty miles an hour! The butterflies travel and eat during the day. When it cools off at night, they rest in trees. The morning sun warms them, and they continue their migration.

Some of the butterflies were traced south across Florida. Many were traced through Texas into Mexico. But there the trail was lost.

Statements:

1. The monarch butterflies have orange-gold, black and white colors on their wings.

2. According to the passage, scientists failed to find the winter home of monarchs from western United States.

3. The Canadian zoologist, Fred Urquhart, spent several decades trying to solve the mystery of the missing monarch butterflies.

4. Urquhart and many volunteers marked thousands of butterflies by attaching tags to them.

5. Each tag bore a code name and the address of Urquhart's Toronto home.

6. The butterflies can fly ten miles an hour and some can even go at eighty miles an hour.

7. The butterflies are actually tougher than we expected.

8. The scientist lost the trail of the butterflies, though some were traced south across Florida and many, through Texas into Mexico.

Part D

The Missing Monarchs (Part Two)

For years Mr. Urquhart and his colleagues wondered where the migratory¹⁷ monarchs spent the winter. Despite their hopes, fieldwork in Florida and along the Gulf¹⁸ Coast discovered no large groups of wintering monarchs. Then in late 1972, his wife Norah wrote to newspapers in Mexico about the project, asking for volunteers to report sightings of the butterfly and help with tagging. Finally, in response came a letter, dated February 26, 1973, from a man called Kenneth Brugger in Mexico City, who offered to help find the butterfly hideaway.

Traveling in his motor home, Brugger drove back and forth¹⁹ across the Mexican countryside, looking for clues. He was especially watchful²⁰ at dusk, when the butterflies would be moving about looking for a place to sleep.

At last, one day was successful. On the evening of January 9, 1975, Brugger called from Mexico. "I have found them -- millions of monarchs -- in evergreens beside a mountain clearing," he said, unable to control the excitement in his voice.

High in a range of volcanic²¹ mountains that crosses central Mexico, he came upon hundreds of evergreen trees, each entirely²² hidden by sleeping butterflies. Some of the insects wore tags that Mr. Urquhart and his helpers had put on them in Canada and the northern United States. The mystery was solved! The monarchs' winter home is well suited to their needs. Throughout the winter the temperature stays near freezing. It is not cold enough to kill the visiting insects, but it is chilly²³ enough to keep them from moving about. The butterflies survive on the stored fat from their summer foods.

In spring the butterflies awaken²⁴ and fly north again. Tagged butterflies, which were marked in Mexico, have been found in the United States.

So one mystery is solved. But another remains²⁵. How do the butterflies find their way? Those that migrate south in the fall were born sometime during the summer or early fall. They have never been to Mexico. Yet they somehow seek out the same resting places. The mystery of how they find their way is left for future scientists to solve.

Questions:

1. What did Mr. Urquhart and his colleagues do in order to find where the monarchs spent the winter?

2. Which of the following is a key condition for the butterflies' winter home?

3. Where do the butterflies sleep?

4. What can we infer about Mr. Urquhart's project according to the passage?

1 foliage   

n.叶子，树叶，簇叶

参考例句：

• The path was completely covered by the dense foliage.小路被树叶厚厚地盖了一层。
• Dark foliage clothes the hills.浓密的树叶覆盖着群山。

2 photosynthesis   

n.光合作用

参考例句：

• In apple trees photosynthesis occurs almost exclusively in the leaves.苹果树的光合作用几乎只发生在叶内。
• Chloroplasts are the structures in which photosynthesis happens.叶绿体就是光合作用发生的地方。

3 maples   

槭树，枫树( maple的名词复数 )； 槭木

参考例句：

• There are many maples in the park. 公园里有好多枫树。
• The wind of the autumn colour the maples carmine . 秋风给枫林涂抹胭红。

4 timing   

n.时间安排，时间选择

参考例句：

• The timing of the meeting is not convenient.会议的时间安排不合适。
• The timing of our statement is very opportune.我们发表声明选择的时机很恰当。

5 shrubs   

灌木( shrub的名词复数 )

参考例句：

• The gardener spent a complete morning in trimming those two shrubs. 园丁花了整个上午的时间修剪那两处灌木林。
• These shrubs will need more light to produce flowering shoots. 这些灌木需要更多的光照才能抽出开花的新枝。

6 pigments   

n.（粉状）颜料( pigment的名词复数 )；天然色素

参考例句：

• The Romans used natural pigments on their fabrics and walls. 古罗马人在织物和墙壁上使用天然颜料。 来自辞典例句
• The original white lead pigments have oxidized and turned black. 最初的白色铅质颜料氧化后变成了黑色。 来自辞典例句

7 steadily   

adv.稳定地；不变地；持续地

参考例句：

• The scope of man's use of natural resources will steadily grow.人类利用自然资源的广度将日益扩大。
• Our educational reform was steadily led onto the correct path.我们的教学改革慢慢上轨道了。

8 vividly   

adv.清楚地，鲜明地，生动地

参考例句：

• The speaker pictured the suffering of the poor vividly.演讲者很生动地描述了穷人的生活。
• The characters in the book are vividly presented.这本书里的人物写得栩栩如生。

9 genetically   

adv.遗传上

参考例句：

• All the bees in the colony are genetically related. 同一群体的蜜蜂都有亲缘关系。
• Genetically modified foods have already arrived on American dinner tables. 经基因改造加工过的食物已端上了美国人的餐桌。 来自英汉非文学 - 生命科学 - 基因与食物

10 evergreen   

n.常青树；adj.四季常青的

参考例句：

• Some trees are evergreen;they are called evergreen.有的树是常青的，被叫做常青树。
• There is a small evergreen shrub on the hillside.山腰上有一小块常绿灌木丛。

11 evergreens   

n.常青树，常绿植物，万年青( evergreen的名词复数 )

参考例句：

• The leaves of evergreens are often shaped like needles. 常绿植物的叶常是针形的。 来自《简明英汉词典》
• The pine, cedar and spruce are evergreens. 松树、雪松、云杉都是常绿的树。 来自辞典例句

12 differentiates   

区分，区别，辨别( differentiate的第三人称单数 )； 区别对待； 表明…间的差别，构成…间差别的特征

参考例句：

• This genus of plants differentiates into many species. 这种植物可分为许多种类。
• Our fax machine differentiates between an incoming fax signal and a voice call. 我们的传真机能区分接收传真信号和语音信号。

13 monarch   

n.帝王，君主，最高统治者

参考例句：

• The monarch's role is purely ceremonial.君主纯粹是个礼仪职位。
• I think myself happier now than the greatest monarch upon earth.我觉得这个时候比世界上什么帝王都快乐。

14 monarchs   

君主，帝王( monarch的名词复数 )

参考例句：

• Monarchs ruled England for centuries. 世袭君主统治英格兰有许多世纪。
• Serving six monarchs of his native Great Britain, he has served all men's freedom and dignity. 他在大不列颠本国为六位君王服务，也为全人类的自由和尊严服务。 来自演讲部分

15 zoologist   

n.动物学家

参考例句：

• Charles darwin was a famous zoologist.查尔斯达尔文是一位著名的动物学家。
• The zoologist had spent a long time living with monkeys.这位动物学家与猴子一起生活了很长时间。

16 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。

17 migratory   

n.候鸟，迁移

参考例句：

• Many migratory birds visit this lake annually.许多候鸟每年到这个湖上作短期逗留。
• This does not negate the idea of migratory aptitude.这并没有否定迁移能力这一概念。

18 gulf   

n.海湾；深渊，鸿沟；分歧，隔阂

参考例句：

• The gulf between the two leaders cannot be bridged.两位领导人之间的鸿沟难以跨越。
• There is a gulf between the two cities.这两座城市间有个海湾。

19 forth   

adv.向前；向外，往外

参考例句：

• The wind moved the trees gently back and forth.风吹得树轻轻地来回摇晃。
• He gave forth a series of works in rapid succession.他很快连续发表了一系列的作品。

20 watchful   

adj.注意的，警惕的

参考例句：

• The children played under the watchful eye of their father.孩子们在父亲的小心照看下玩耍。
• It is important that health organizations remain watchful.卫生组织保持警惕是极为重要的。

21 volcanic   

adj.火山的；象火山的；由火山引起的

参考例句：

• There have been several volcanic eruptions this year.今年火山爆发了好几次。
• Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。

22 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

23 chilly   

adj.凉快的，寒冷的

参考例句：

• I feel chilly without a coat.我由于没有穿大衣而感到凉飕飕的。
• I grew chilly when the fire went out.炉火熄灭后，寒气逼人。

24 awaken   

vi.醒，觉醒；vt.唤醒，使觉醒，唤起，激起

参考例句：

• Old people awaken early in the morning.老年人早晨醒得早。
• Please awaken me at six.请于六点叫醒我。

25 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。