2009年英语六级最新模拟试题卷（第5组）速读

Part ⅡReading Comprehension (Skimming and Scanning) (15 minutes)

Rain forests
Tropical rainforests are the most diverse ecosystem (生态系统) on Earth, and also the oldest. Today, tropical rainforests cover only 6 percent of the Earth's ground surface, but they are home to over half of the planet’s plant and animal species。

What Is a Rainforest?
Generally speaking, a rainforest is an environment that receives high rainfall and is dominated by tall trees. A wide range of ecosystems fall into this category, of course. But most of the time when people talk about rainforests, they mean the tropical rainforests located near the equator。

These forests receive between 160 and 400 inches of rain per year. The total annual rainfall is spread pretty evenly throughout the year, and the temperature rarely dips below 60 degrees Fahrenheit。

This steady climate is due to the position of rainforests on the globe. Because of the orientation of the Earth's axis, the Northern and Southern hemispheres each spend part of the year tilted away from the sun. Since rainforests are at the middle of the globe, located near the equator, they arc not especially affected by this change. They receive nearly the same amount of sunlight, and therefore heat, all year. Consequently, the weather in these regions remains fairly constant。

The consistently wet, warm weather and ample sunlight give plant life everything it needs to thrive. Trees have the resources to grow to tremendous heights, and they live for hundreds, even thousands, of years. These giants, which reach 60 to 150 ft in the air, form the basic structure of the rainforest. Their top branches spread wide in order to capture maximum sunlight. This creates a thick canopy (树冠) level at the top of the forest, with thinner greenery levels underneath. Some large trees grow so tall that they even tower over the canopy layer。

As you go lower, down into the rainforest, you find less and less greenery. The forest floor is made up of moss, fungi, and decaying plant matter that has fallen from the upper layers. The reason for this decrease in greenery is very simple the overabundance of plants gathering sunlight at the top of the forest blocks most sunlight from reaching the bottom of the forest, for robust plants to thrive。

The, Forest for the Trees
The ample sunlight and extremely wet climate of many tropical areas encourage the growth of towering trees with wide canopies. This thick top layer of the rainforest dictates the lives of all other plants in the forest. New tree seedlings rarely survive to make it to the top unless some older trees die, creating a "hole" in the canopy. When this happens, all of the seedlings on the ground level compete intensely to reach the sunlight。

Many plant species reach the top of the forest by climbing the tall trees. It is much easier to ascend this way, because the plant doesn't have to form its own supporting structure。

Some plant species, called epiphytes, grow directly on the surface of the giant trees. These plants, which include a variety of orchids and ferns, make up much of the understory, the layer of the rainforest right below the canopy. Epiphytes are close enough to the top to receive adequate light, and the runoff from the canopy layer provides all the water and nutrients(养分)they need, which is important since they don't have access to the nutrients in the ground。

Stranglers and Buttresses
Some epiphytes eventually develop into stranglers. They grow long, thick roots that extend down the tree trunk into the ground. As they continue to grow, the roots form a sort of web structure all around the tree. At the same time, the strangler plant's branches extend upward, spreading out into the canopy. Eventually, the strangler may block so much light from above, and absorb such a high percentage of nutrients from the ground below, that the host tree dies。

Competition over nutrients is almost as intense as competition for light. The excessive rainfall rapidly dissolves nutrients in the soil making it relatively infertile except at the top layers. For this reason, rainforest tree roots grow outward to cover a wider area, rather than downward to lower levels. This makes rainforest trees somewhat unstable, since they don't have very strong anchors in the ground. Some trees compensate for this by growing natural buttresses. These buttresses are basically tree trunks that extend out from the side of the tree and clown to the ground, giving the tree additional support。

Rainforest trees are dependent on bacteria that are continually producing nutrients in the ground. Rainforest bacteria and trees have a very close, symbiotic (共生的) relationship. The trees provide the bacteria with food, in the form of fallen leaves and other material, and the bacteria break this material down into the nutrients that the survive。

One of the most remarkable things about rainforest plant life is its diversity. The temperate rainforests of the Pacific Northwest are mainly composed of a dozen or so tree species. A tropical rainforest, on the other hand, might have 300 distinct tree species。

All Creatures, Great and Small
Rainforests are home to the majority of animal species in the world. And a great number of species who now live in other environments, including humans, originally inhabited the rainforests. Researchers estimate that in a large rainforest area, there may be more than 10 million different animal species。

Most of these species have adapted for life in the upper levels of the rainforest, where food is most plentiful. Insects, which can easily climb or fly from tree to tree, make up the largest group (ants are the most abundant animal in the rainforest). Insect species have a highly symbiotic relationship with the plant life in a rainforest. The insects move from plant to plant, enjoying the wealth of food provided there. As they travel, the insects may pick up the plants' seeds, dropping them some distance away. This helps to disperse the population of the plant species over a larger area。

The numerous birds of the rainforest also play a major part in seed dispersal. When they eat fruit from a plant, the seeds pass through their digestive system. By the time they excrete (排泄) the seeds, the flown many miles away from the fruit-bearing tree。

There are also a large number of reptiles and mammals in the rainforest. Since the weather is so hot and humid during the day, most rainforest mammals are active only at night, dusk or dawn. The many rainforest bat species are especially well adapted for this lifestyle. Using their sonar, bats navigate easily through the mass of trees in the rainforest, feeding on insects and fruit。

While most rainforest species spend their lives in the trees, there is also a lot of life on the forest floor. Great apes, wild pigs, big cats and even elephants can all be found in rainforests. There are a number of people who live in the rainforests, as well. These tribes--which, up until recently, numbered in the thousands--are being forced out of the rainforests at an alarming rate because of deforestation。

Deforestation
In the past hundred years, humans have begun destroying rainforests at an alarming rate. Today, roughly 1.5 acres of rainforest are destroyed every second. People are cutting down the rainforests in pursuit of three major resources:
· land for crops
· lumber for paper and other wood products
· land for livestock pastures

In the current economy, people obviously have a need for all of these resources. But almost all experts agree that, over time, we will suffer much more from the destruction of the rainforests than we will benefit。

The world's rainforests are an extremely valuable natural resource, to be sure, but not for their lumber or their land. They are the main cradle of life on Earth, and they hold millions of unique life forms that we have yet to discover. Destroying the rainforests is comparable to destroying an unknown planet we have no idea what we're losing. If deforestation continues at its current rate, the world's tropical rainforests will be wiped out within 40 years。

1. Virtually all plant and animal species on Earth can be found in tropical rainforests。
2. There is not much change in the weather in the tropical rainforests all the year round。
3. The largest number of rainforests in the world are located on the African continent。
4. Below the canopy level of a tropical rainforest grows an overabundance of plants。
5. New tree seedlings will not survive to reach the canopy level unless ______。
6. Epiphytes, which form much of the understory of the rainforest, get all their water and nutrients from ______。
7. Stranglers are so called because they ______ by blocking the sunlight and competing for the nutrients。
8. Since rainforest bacteria and trees depend on each other for life, the relationship they form is termed ______。
9. Plant species are dispersed over a large area with the help of ______。
10. As we are still ignorant of millions of unique life forms in the rainforest, deforestation can be compared to the destruction of ______。

Part Ⅱ Reading Comprehension (Skimming and Scanning)
1. N 第一段第二句“Today, tropical rainforests cover only 6 percent of the Earth's ground surface，but they are home to over half of the planet's plant and animal species”中提到，热带雨林占全球面积的6%，却拥有超过地球一半以上的动植物种类。这句话表明，不是所有动在热带雨林中找到，比如很多海洋生物就不能在热带雨林中找到。
2.根据“What Is a Rainforest?”部分第三段中的“Since rainforests are at the middle of the globe，located near the equator，they are not especially affected by this change.They receive nearly the same amount of sunlight，and therefore heat，all year.Consequently，the weather in these regions remains fairly constant”，此说法是正确的。
3.文中并未提及哪里拥有最多、林，只讲到热带雨林通常在赤道附近，常年炎热、降水充分、物种丰富。
4.由“What Is a Rainforest?”部分最后一段中的两句话“As you go lower，down into the rainforest，you find less and less greenery。”和“The overabundance of plants gathering sunlight at the top of the forest blocks most sunlight from reaching the bottom of the forest，, for robust plants to thrive。”可见，由于浓密的树冠层挡住了大部分阳光，地面的植被并不茂盛。所以，题中说法是错误的。
5.“The Forest for the Trees”部分第一段中的“New tree seedlings rarely survive to make is to the top unless some older trees die，creating a “hole” in the canopy。”因此，答案是“some older trees die”。只有老树死亡后，新的树苗才能成活，向上生长，到达树冠层。
6.“The Forest for the Trees”部分最后一段中提到“Epiphytes are close enough to the top to receive adequate light，and the runoff from the canopy layer provides all the water and nutrients they need，which is important since they don't have access to the nutrients in the ground。”可供水和养分的是树冠层。故正确答案为“the canopy layer”。
7.由“Strangler and Buttresses”部分的第一段最后一句“Eventually，the strangler may block so much light from above，and absorb such a high percentage of nutrients from the ground below， that the host tree dies。”可见附生植物最终导致宿主树木死亡。故答案为“kill the host tree”。
8.由“Strangler and Buttresses”部分的第三段中的“Rainforest bacteria and trees have a very close，symbiotic relationship.The trees provide the bacteria with fond，in the form of fallen leaves and other material，and the bacteria break this material down into the nutrients that the survive。”可知树木为细菌提供食物，细菌则分解这些东西，反过来为树木提供养分。它们之间是密切的共生关系。故答案为“symbiotic”。
9.由“All Creatures，Great and Small”部分第二段“As they travel，the insects may pick up the plants' seeds，dropping them some distance away。”和第三段“This helps to disperse the population of the plant species over a larger area.By the time they excrete the seeds，the flown many miles away from the fruit-bearing tree，”可见昆虫和鸟类都能帮助植物传播种子。雨林中生活的大量动物其实也帮助植物传播种子。所以，答案可以是“insects and birds/insects/birds/animals”。
10.由“Deforestation”部分的最后一段“Destroying the rainforests is comparable to destroying an unknown planet—we have no idea what we're losing。”可知正确答案为“an unknown planet”。