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Sometime early in the next century, human beings will move to Mars. They will live there for about a year, and then will be replaced with another group of pioneers. Building the base on Mars will advance our knowledge of the solar system and aid in our understanding of the earth.
We already know that Mars resembles the earth in many aspects: general size, presence of water, length of day, range of temperatures. These resemblances have caused many people to consider a centuries-long project: to terraform Mars. Terraforming means altering a planet’s surface so that Earth’s life forms can survive there. This concept, previously found only in science fiction is now being seriously considered by scientists.
Terraforming Mars is theoretically simple: add nitrogen and oxygen to the atmosphere; pump water to the surface; and add the earth’s plants and animals in the order in which they developed on Earth. But it will take at least 300 years.
Some people think that such a project is too huge for humans to undertake, but there are very good reasons to make the attempt. The earth now contains some 6 billion people, and no one has any idea of how many humans the earth can support. Our very existence and numbers are threatening many other species. We also have had some experience with terraforming our own planet: altering the landscape, the atmosphere and the climate. Currently terraforming earth has become a wiser activity as we try to control global warming, air and water pollution, and preserve some natural living places.
41．What would be the best title for this passage?
A．Terraforming Mars. B．Saving the Earth.
C．Travelling to Mars. D．A Newly-found Place.
42．What does the underlined word “altering” mean in the second paragraph?
A．Warming. B．Changing. C．Planting. D．Building.
43．According to the passage the main purpose of terraforming Mars is to ________.
A．do some scientific research work
B．find out its similarity to earth
C．avoid the dying away of many other species
D．find on Mars living place for the increasing human beings
44．The main reason for causing many people to consider terraforming Mars is that _______.
A．there are some resemblances between Earth and Mars.
B．terraforming Mars is theoretically simple
C．we have had some experience with terraforming our own planet: Earth
D．the development of science and technology is very rapid
45．What’s the author’s attitude towards the project?
A．Optimistic. B．Negative. C．Sceptical（怀疑的）. D．Objective.
查看习题详情和答案>>away or fight back. Plants certainly cannot run away, and they lack teeth and claws. But plants can
defend (保护) themselves by using both physical and chemical means.
Some plants have their own ways to keep animals away. For example, the leaves of the holly plant
have sharp spines (刺) that discourage grass-eating animals. Holly leaves on lower branches have more
spines than leaves on upper branches. This is because the lower leaves are easier for most animals to
reach.
Some plants, such as the oak tree, have thick and hard leaves that are difficult for animals to eat. Some
grasses may contain a sandy material; eating such grasses wears down the animal's teeth.
Many plants also have chemical defenses. Some plants produce chemicals that taste bitter or cause an
unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a caterpillar (毛虫) bites a tobacco leaf, the leaf produces a chemical messenger. This messenger sends to the roots the information to produce more nicotine. The higher levels of nicotine discourage the
caterpillar.
Many plants depend on both physical and chemical defenses. A certain plant in China, for instance,
has prickly (多刺的) leaves, and each prickle contains poisonous venom (毒液) A single experience with
this kind of plant will teach an animal to stay away from it in the future.
B. physical means
C. bitter chemicals
D. sandy materials
B. Its roots send a messenger to discourage the caterpillar.
C. Its roots increase the production of nicotine when it is attacked.
D. Its leaves produce poisonous sand to drive the caterpillar away.
B. How Plants Defend Themselves
C. Attacks and Defenses
D. How Animals Eat Plant Leaves
Sometime early in the next century, human beings will move to Mars. They will live there for about a year, and then will be replaced with another group of pioneers. Building the base on Mars will advance our knowledge of the solar system and aid in our understanding of the earth.
We already know that Mars resembles the earth in many aspects: general size, presence of water, length of day, range of temperatures. These resemblances have caused many people to consider a centuries-long project: to terraform Mars. Terraforming means altering a planet’s surface so that Earth’s life forms can survive there. This concept, previously found only in science fiction is now being seriously considered by scientists.
Terraforming Mars is theoretically simple: add nitrogen and oxygen to the atmosphere; pump water to the surface; and add the earth’s plants and animals in the order in which they developed on Earth. But it will take at least 300 years.
Some people think that such a project is too huge for humans to undertake, but there are very good reasons to make the attempt. The earth now contains some 6 billion people, and no one has any idea of how many humans the earth can support. Our very existence and numbers are threatening many other species. We also have had some experience with terraforming our own planet: altering the landscape, the atmosphere and the climate. Currently terraforming earth has become a wiser activity as we try to control global warming, air and water pollution, and preserve some natural living places.
While the possibility of such a project is small, it is not impossible. Even if earth-bound societies come and go in the next 300 years, the project can continue through the work of the Mars settlers without the need for constant backing from the earth.
The future existence of all the people in our world may very well depend upon our ability to terraform Mars.
What would be the best title for this passage?
A．Terraforming Mars. B．Saving the Earth.
C．Travelling to Mars. D．A Newly-found Place.
What does the underlined word “altering” mean in the second paragraph?
A．Warming. B. Changing. C. Planting. D. Building.
According to the passage the main purpose of terraforming Mars is to ___________ .
A．do some scientific research work
B．find out its similarity to earth
C．avoid the dying away of many other species
D．find on Mars living place for the increasing human beings
The main reason for causing many people to consider terraforming Mars is that _________ .
A．there are some resemblances between Earth and Mars.
B．terraforming Mars is theoretically simple
C．we have had some experience with terraforming our own planet: Earth
D．the development of science and technology is very rapid
What’s the author’s attitude towards the project?
A．Optimistic B．Negative. C. Skeptical（怀疑的） D．Objective.
查看习题详情和答案>>Sometime early in the next century, human beings will move to Mars. They will live there for about a year, and then will be replaced with another group of pioneers. Building the base on Mars will advance our knowledge of the solar system and aid in our understanding of the earth.
We already know that Mars resembles the earth in many aspects: general size, presence of water, length of day, range of temperatures. These resemblances have caused many people to consider a centuries-long project: to terraform Mars. Terraforming means altering a planet’s surface so that Earth’s life forms can survive there. This concept, previously found only in science fiction is now being seriously considered by scientists.
Terraforming Mars is theoretically simple: add nitrogen and oxygen to the atmosphere; pump water to the surface; and add the earth’s plants and animals in the order in which they developed on Earth. But it will take at least 300 years.
Some people think that such a project is too huge for humans to undertake, but there are very good reasons to make the attempt. The earth now contains some 6 billion people, and no one has any idea of how many humans the earth can support. Our very existence and numbers are threatening many other species. We also have had some experience with terraforming our own planet: altering the landscape, the atmosphere and the climate. Currently terraforming earth has become a wiser activity as we try to control global warming, air and water pollution, and preserve some natural living places.
While the possibility of such a project is small, it is not impossible .Even if earth –bound societies come and go in the next 300 years, the project can continue through the work of the Mars settlers without the need for constant backing from the earth.
The future existence of all the people in our world may very well depend upon our ability to terraform Mars.
1.What would be the best title for this passage?
A．Terraforming Mars. B．Saving the Earth
C．Travelling to Mars. D．A Newly-found Place
2.What does the underlined word “altering” mean in the second paragraph?
A．Warming. B．Changing. C．Planting. D．Building
3.According to the passage the main purpose of terraforming Mars is to ________.
A．do some scientific research work
B．find out its similarity to earth
C．avoid the dying away of many other species
D．find on Mars living place for the increasing human beings
4.The main reason for causing many people to consider terraforming Mars is that _______.
A．there are some resemblances between Earth and Mars.
B．terraforming Mars is theoretically simple
C．we have had some experience with terraforming our own planet: Earth
D．the development of science and technology is very rapid
5.What’s the author’s attitude towards the project?
A．Optimistic. B．Negative
C．Sceptical（怀疑的） D．Objective.
查看习题详情和答案>>
Sometime early in the next century, human beings will move to Mars. They will live there for about a year, and then will be replaced with another group of pioneers. Building the base on Mars will advance our knowledge of the solar system and aid in our understanding of the earth.
We already know that Mars resembles the earth in many aspects：general size, presence of water, length of day, range of temperatures. These resemblances have caused many people to consider a centuries-long project：to terraform Mars. Terraforming means altering a planet’s surface so that Earth’s life forms can survive there. This concept, previously found only in science fiction is now being seriously considered by scientists.
Terraforming Mars is theoretically simple：add nitrogen and oxygen to the atmosphere; pump water to the surface; and add the earth’s plants and animals in the order in which they developed on Earth. But it will take at least 300 years.
Some people think that such a project is too huge for humans to undertake, but there are very good reasons to make the attempt. The earth now contains some 6 billion people, and no one has any idea of how many humans the earth can support. Our very existence and numbers are threatening many other species. We also have had some experience with terraforming our own planet：altering the landscape, the atmosphere and the climate. Currently terraforming earth has become a wiser activity as we try to control global warming, air and water pollution, and preserve some natural living places.
While the possibility of such a project is small, it is not impossible. Even if earth-bound societies come and go in the next 300 years, the project can continue through the work of the Mars settlers without the need for constant backing from the earth.
he future existence of all the people in our world may very well depend upon our ability to terraform Mars.
1．What would be the best title for this passage?
A．Terraforming Mars. B．Saving the Earth.
C．Travelling to Mars. D．A Newly-found Place.
2．What does the underlined word “altering” mean in the second paragraph?
A． Warming. B．Changing. C．Planting. D．Building.
3．According to the passage the main purpose of terraforming Mars is to _________.
A．do some scientific research work
B．find out its similarity to earth
C．avoid the dying away of many other species
D．find on Mars living place for the increasing human beings
4．What’s the author’s attitude towards the project?
A．Optimistic． B．Negative.
C．Doubtful D．Objective.
查看习题详情和答案>>