Big trees are incredibly important ecologically. For a start, they provide food for countless other species and shelter for many animals. With their tall branches in the sun, they capture vast amounts of energy. This allows them to produce massive crops of fruit and flowers that sustain much of the animal life in the forest.

Only a small number of tree species have the genetic ability to grow really big. The biggest are native to North America, but big trees grow all over the globe, from the tropics to the forests of the high latitudes (纬度). To achieve giant size, a tree needs three things: the right place to establish its seedling, good growing conditions and lots of time with low adult death rate. Lose any of these, and you will lose your biggest trees.

In some parts of the world, populations of big trees are dwindling(逐渐变少) because their seedlings cannot survive. In southern India, for instance, an aggressive non-native bush, Lantana camara, is invading the floor of many forests. Lantana grows so thickly that young trees often fail to take root. With no young trees to replace them, it is only a matter of time before most of the big trees disappear.

Without the right growing conditions, trees cannot get really big and there is some evidence to suggest tree growth could slow in a warmer world, particularly in environments that are already warm. Having worked for decades at La Selva Biological Station in Puerto Viejo de Sarapiqui, Costa Rica, David and Deborah Clark and colleagues have shown that tree growth there declines markedly in warmer years. “During the day, their growth shuts down when it gets too warm, and at night they consume more energy because their metabolic (新陈代谢) rate increases,” explains David Clark. With less energy produced in warmer years and more being consumed just to survive, there is even less energy available for growth.

The darks’ theory, if correct, means tropical forests would shrink over time. The largest, oldest trees would progressively die off and tend not to be replaced. According to the Clarks, this might cause a destabilization(不稳定) of the climate; as older trees die, forests would release some of their stored carbon into the atmosphere, causing a cycle of further warming, forest shrinkage and carbon emissions.

Besides, big trees face threats from elsewhere.

1.According to the passage, big trees make great contributions to the ecosystem because .

A. they can capture large amounts of energy.

B. they determine the change of global climate.

C. they provide the essentials for many creatures.

D. they can avoid a new cycle of further warming.

2.All the following factors are a must for making big trees EXCEPT .

A. no deadly damage

B. genetic contribution

C. ideal environment for growth

D. high-latitude location

3. What is the best title of the passage?

A. Big trees in trouble.

B. Advantages of big trees.

C. Results of big trees’ disappearing.

D. Importance of big trees to humans.

4.What will the author most probably discuss after the last paragraph?

A. More threats to the existence of big trees.

B. The effect of human activities on big trees.

C. Benefits of big trees to the whole atmosphere.

D. Comparison between common trees and big ones.

Volunteers Wanted

Ecuador

A village in Ecuador has recently developed a ecotourism (生态旅游) project that needs volunteers with a background in tourism. This is an unpaid, challenging job that might last one year. You must be enthusiastic and speak good level of Spanish. You will need to cover your food and lodging on your own.

To find out more information, e-mail volunteer@ ecuador.org.

Bali

Would you like to teach English or computer skills to our local school children in a lovely village in the mountains of Bali? There are also western children homeschooling here, some of whom need help with their daily programs. For volunteers of homeschooling, you are required to have baby-sitter experience. Please contact me for more information at Bali@yahoo.com.

Dominica

Experience nature and adventure in Dominica, the island of the Caribbean. Be part of a happy team, doing things from gardening, to building tree houses, to maintaining hydro systems.

For more information please e-mail info@Dominica.com.

1.A college graduate who speaks good Spanish and is interested in ecotourism had better work in ______.

A. an island of Dominica B. a village in Ecuador

C. the mountains of Bali D. a house in Caribbean

2.One who wants to teach small children English will contact ______.

A. volunteer@org B. info@Dominica.com

C. volunteer@ ecuador.org D. Bali@yahoo.com

3.Which is NOT a required task for a volunteer at the island of Dominica?

A. Gardening.

B. Building tree houses.

C. Swimming in the pool.

D. Maintaining hydro systems.

Item 78431 The Video Camera Pen

$129. 95 ;Available for Immediate Shipment; Order by Phone :1-800-321-1484

This is the pen that has a built-in video camera, capturing(拍摄,录制)videos or still images with a click of its button. Ideal for use while secured in a pocket, it can capture up to five hours of video. Its battery provides up to two hours of power before requiring a recharge.

Item 78098 The Wristwatch Camcorder

$149. 95; Available for 3-day Shipment; Order by Phone :1-800-321-1484

This is the men's watch with an unnoticeable camera located at the two-o'clock position, yet the watch's hands never make it covered. So you'll be always ready to capture a famous person or a pet's ridiculous actions. The camera's rechargeable battery provides up to two hours of use from a four-hour charge.

Item 77918 The only 55 Inch Widescreen Personal Movie Theater

$ 249. 95 ;Available for Immediate Shipment; Order by Phone:l-800-321-1484

This is the only personal media viewer that provides a private viewing experience just like watching a widescreen 55 inch television from 10 meters away. It connects to a video iPod, iPhone, portable DVD player with two AA batteries providing up to six hours of continuous operation.

Item 77281 The Digital Phone Album Watch

$ 99. 95 ;Available for Immediate Shipment; Order by Phone :1-800-321-1484

This is the watch that vividly displays 120 of your favorite digital photographs. You can download digital photographs to the watch. The watch can be viewed in the Photo Album mode (模式) or digital mode( time and date view). A six-hour charge provides up to 10 days of use.

1.What's the purpose of this passage?

A. To advertise some goods.

B. To compare some goods.

C. To teach how to operate the items

D. To show how fashionable the items are.

2.What do Item 7.8431 and Item 78098 have in common according to this passage?

A. They both sell well.

B. They both can take photos.

C. They both have unusual appearances.

D. They are both cheap.

3. If you're a movie fan, you probably show strong interest in .

A. Item 78098 B. Item 78431

C. Item 77281 D. Item 77918

4.Which of the following is TRUE according to the passage?

A. In fact, Item 78098 cannot tell time.

B. Item 77918 works as a DVD player.

C. In a way, Item 77281 is user-friendly

D. All the items include rechargeable batteries.

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