Which one is NOT the role of Amazon rainforest in the earth ecosystem？

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, making it difficult 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.

&

A．Y

B．N

C．NG

Rainforests

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 tress. 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 neat the equator.

These forests raceive 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 golbe. 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 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.

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 It 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 plandts gathering sunlight at the top of the forest blocks most sunlight from reaching the bottom of the forest, making it difficult 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 in 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 does's have to form. its own supporting structure.

Some plant species, called epiphytes, grow directly on the surface of the giant tress. 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.

tranglers and Buttresses

Same epiphytes eventually develop into stranglers. They grow long, thick roots that extend down the tree trunk into the

A．Y

B．N

C．NG

Rainforests

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 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.

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, making it difficult 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 cane by. 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 under story, the layer of the rain forest fight 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

A．Y

B．N

C．NG

Which one is NOT the source of renewable energy?

A．Wind.

B．Sunlight.

C．Tides.

D．Rain.

The atmosphere and oceans are not the only parts of the environment being damaged. Rain forests are being quickly destroyed as well, and their survival is questionable. E. O. Wilson, a biologist at Harvard, calls the depletion(枯竭、耗尽)of rain forest areas "the greatest extinction since the end of the age of dinosaurs (恐龙)"

Unlike some environmental issues, rain forest depletion has fortunately received significant public and media attention. Despite the opposition to the cutting down of rain forests, the problem continues. Every year, Brazil chops down on area of forest the size of the state of Nebraska. In addition to the Amazon's rain forests, many other forests are being cut down as well. In Indonesia, Zaire, Papua New Guinea, Malaysia, Burme, the Philippines peru, Colombia, Bolivia, and Venezuela, rain forests that were once great have been lost.

According to some estimates, 50 million acres of rain forest are cut down every year. The United Nations says the figure is closer to 17 million acres. The World Wildlife Fund says that every minute, 25 to 50 acres are cut or burned to the ground.

The world's growing population has been a primary reason of rain forest destruction. More people need land to live on and wood products to consume. Limiting population growth may be the first in a series of steps that would limit the destruction of the rain forests.

In the opinion of the author, ______ are being destroyed terribly at present.

A．the oceans

B．the atmosphere

C．the rain forests

D．all the above

The atmosphere and oceans are not the only parts of the environment being damaged. Rain forests are being quickly destroyed as well, and their survival is questionable. E. O. Wilson, a biologist at Harvard, calls the depletion(枯竭、耗尽)of rain forest areas "the greatest extinction since the end of the age of dinosaurs(恐龙)."

Unlike some environmental issues, rain forests' depletion has fortunately received significant public and media's attention. Despite the opposition to the cutting down of rain forests, the problem continues. Every year, Brazil chops down an area of forests the size of the state of Nebraska. In addition to the Amazon's rain forests, many other forests are being cut down as well.: In Indonesia, Zaire, Papua-new Guinea, Malaysia, Burme, the Philippines, Peru, Colombia, Bolivia, and Venezuela, rain forests that were once great have been lost.

According to some estimates, 50 million acres of rain forest are cut down every year. The United Nations says the figure is closer to 17 million acres. The World Wildlife Fund says that every minute,25 to 50 acres are cut down or burnt to the ground.

The world's growing population has been a primary reason of rain forests' destruction. More people need land to live on and wood products to consume. Limiting population growth may be the first in a series of steps that would alleviate the destruction of the rain forests.

In the opinion of the author, ______are being destroyed terribly at present.

A．the oceans

B．the atmosphere

C．the rain forests

D．all the above

What does the last sentence of the passage most probably mean?

A．The rainforest in the Central African Republic will be preserved forever.

B．The well-designed exhibit will be preserved as an artifact.

C．The exhibit reflects the hope that natural rainforests will be well preserved.

D．The exhibit of the rainforest in the museum is the sole one in the world.

Passage Four

The atmosphere and oceans are not the only parts of the environment being damaged. Rain forests are being quickly destroyed as well, and their survival is questionable. E. O. Wilson, a biologist at Harvard, calls the depletion(枯竭、耗尽)of rain forest areas "the greatest extinction since the end of the age of dinosaurs(恐龙)."

Unlike some environmental issues, rain forests' depletion has fortunately received significant public and media's attention. Despite the opposition to the cutting down of rain forests, the problem continues. Every year, Brazil chops down an area of forests the size of the state of Nebraska. In addition to the Amazon's rain forests, many other forests are being cut down as well.: In Indonesia, Zaire, Papua-new Guinea, Malaysia, Burme, the Philippines, Peru, Colombia, Bolivia, and Venezuela, rain forests that were once great have been lost.

According to some estimates, 50 million acres of rain forest are cut down every year. The United Nations says the figure is closer to 17 million acres. The World Wildlife Fund says that every minute,25 to 50 acres are cut down or burnt to the ground.

The world's growing population has been a primary reason of rain forests' destruction. More people need land to live on and wood products to consume. Limiting population growth may be the first in a series of steps that would alleviate the destruction of the rain forests.

48. In the opinion of the author, ______are being destroyed terribly at present.

A. the oceans

B. the atmosphere

C. the rain forests

D. all the above

Water on the earth is being continuously recycled in a process known as the hydrologic cycle. The first step of the cycle is the evaporation of water in the oceans. Evaporation is the process of water turning into vapor ,which then forms clouds in the sky. The second step is the water returning to the earth in the form. of precipitation, either rain, snow, or ice. When the water reaches the earth's surface, it runs off into the rivers, lakes, and the ocean, where the cycle begins again.

Not all water, however, stays on the surface of the earth in the hydrologic cycle. Some of it seeps (渗透) into the ground through infiltration and collects under the earth's surface as groundwater. This groundwater is extremely important to life on earth since 95% of the earth's water is in the oceans, and is too salty for humans of plants. Of the 5% on land, only 0.05% is above ground in rivers or lakes. The rest is underground. water. This groundwater is plentiful and dependable, as it doesn't depend on seasonal rain or snow. It is the major source of water for many cities. But as the population increases and the need for water also increases, the groundwater in some areas is getting dangerously low. Added to this problem is an increasing amount of pollution that seeps into the groundwater. In the future, with an increasing population and more toxic(有毒)waste, the hydrologic cycle we depend on could become dangerously imbalanced.

The best title for this passage is ______.

A．Water Conservation

B．The Hydrologic Cycle

C．Underground Water

D．Polluted Groundwater

The geology of the Earth's surface is dominated by the particular properties of water. Present on Earth in solid, liquid, and gaseous states, water is exceptionally reactive. It dissolves, transports, and precipitates many chemical compounds and is constantly modifying the face of the Earth.

Evaporated from the oceans, water vapor forms clouds, some of which are transported by wind over the continents. Condensation from the clouds provides the essential agent of continental erosion: rain. Precipitated onto the ground, the water trickles down to form. brooks, streams, and rivers, constituting what is called the hydrographic network. This immense polarized network channels the water toward a single receptacle: an ocean. Gravity dominates this entire step in the cycle because water tends to minimize its potential energy by running from high altitudes toward the reference point that is sea level.

The rate at which a molecule of water passes through the cycle is not random but is a measure of the relative size of the various reservoirs. If we define residence time as the average time for a water molecule to pass through one of the three reservoirs--atmosphere, continent, and ocean--we see that the times are very different. A water molecule stays, on an average, eleven days in the atmosphere, one hundred years on a continent and forty thousand years in the ocean. This last figure shows the importance of the ocean as the principal reservoir of the hydrosphere but also the rapidity of water transport on the continents.

A vast chemical separation process takes places during the flow of water over the continents. Soluble ions such as calcium, sodium, potassium, and some magnesium are dissolved and transported. Insoluble ions such as aluminum, iron, and silicon stay where they are and form. the thin, fertile skin of soil on which vegetation can grow. Sometimes soils are destroyed and transported mechanically during flooding. The erosion of the continents thus results from two closely linked and interdependent processes, chemical erosion and mechanical erosion. Their respective interactions and efficiency depend on different factors.

According to the passage, clouds are primarily formed by water ______.

A．precipitating onto the ground

B．changing from a solid to a liquid state

C．evaporating from the oceans

D．being carried by wind