A weather map is an important tool for geographers. A succession of three of four maps presents a continuous picture of weather changes. Weather forecasts are able to determine the speed of air masses and fronts; to determine whether an individual pressure area is deepening or becoming shallow and whether a front is increasing or decreasing in intensity. They are also able to determine whether an air mass is retaining its original characteristics or taking on those of the surface over which it is moving. Thus, a most significant function of the map is to reveal a synoptic picture of conditions in the atmosphere at a given time.
All students of geography should be able to interpret a weather map accurately. Weather maps contain an enormous amount of information about weather conditions existing at the time of observation over a large geographical area. They reveal in a few minutes what otherwise would take hours to describe. The United States weather Bureau issues information about approaching storms, floods, frosts, droughts, and all climatic conditions in general. Twice a month it issues a 30-day "outlook" which is a rough guide to weather conditions likely to occur over broad areas of the United States. These 30-day outlooks are based upon an analysis of the upper air levels with often set the stage for the development of air masses, fronts, and storms.
Considerable effort is being exerted today to achieve more accurate weather predictions. With the use of electronic instruments and earth satellites, enormous gains have taken place recently in identifying and tracking storms over regions which have but few meteorological stations. Extensive experiments are also in progress for weather modification studies. But the limitations of weather modification have prevented meteorological results except in the seeding of super-cooled, upslope mountainous winds which have produced additional orographical precipitation on the windward side of mountain ranges. Nevertheless, they have provided a clearer understanding of the fundamentals of weather elements.
One characteristic of weather maps not mentioned by the author in this passage is______.

A:wind speed B:thermal changes C:fronts D:barometric pressure

A weather map is an important tool for geographers. A succession of three of four maps presents a continuous picture of weather changes. Weather forecasts are able to determine the speed of air masses and fronts; to determine whether an individual pressure area is deepening or becoming shallow and whether a front is increasing or decreasing in intensity. They are also able to determine whether an air mass is retaining its original characteristics or taking on those of the surface over which it is moving. Thus, a most significant function of the map is to reveal a synoptic picture of conditions in the atmosphere at a given time.
All students of geography should be able to interpret a weather map accurately. Weather maps contain an enormous amount of information about weather conditions existing at the time of observation over a large geographical area. They reveal in a few minutes what otherwise would take hours to describe. The United States weather Bureau issues information about approaching storms, floods, frosts, droughts, and all climatic conditions in general. Twice a month it issues a 30-day "outlook" which is a rough guide to weather conditions likely to occur over broad areas of the United States. These 30-day outlooks are based upon an analysis of the upper air levels with often set the stage for the development of air masses, fronts, and storms.
Considerable effort is being exerted today to achieve more accurate weather predictions. With the use of electronic instruments and earth satellites, enormous gains have taken place recently in identifying and tracking storms over regions which have but few meteorological stations. Extensive experiments are also in progress for weather modification studies. But the limitations of weather modification have prevented meteorological results except in the seeding of super-cooled, upslope mountainous winds which have produced additional orographical precipitation on the windward side of mountain ranges. Nevertheless, they have provided a clearer understanding of the fundamentals of weather elements.

One characteristic of weather maps not mentioned by the author in this passage is（）

A:wind speed B:thermal changes C:fronts D:barometric pressure

A wind tunnel is used for testing planes or plane models. In a wind tunnel air is blown over a plane or a model placed in a test section. Wind tunnel test sections are different in size depending on airflow speed requirements. Some low-speed tunnels have test sections large enough for a complete small plane. In the very high speed tunnels used for space testing, however, the model may be as small as a pencil.
There are two ways of feeding air to the test section. In the constant flow tunnel, airflow produced by electric fans is forced through the tunnel to the test section, then through another tunnel section back to the starting point for reuse. The other way involves storing high-pressure air in a box, sending it out by a controlling device to pass through the tunnel and test section into another box. This way is usually used for a very short period of high-speed airflow.
Wind tunnels are usually used to test planes before they are flown. Problems in a plane can be found when it meets the high-speed airflow in the tunnel. For example, if the wings are built so that they would weaken at high speeds, this fact can be discovered in the tunnel, thus saving many lives and millions of dollars.
In a wind tunnel, scientists also find out how different planes will act at different speeds. They find out such things as how the air dives by the wing surfaces, how slowly a plane can fly before it starts to drop, and how fast it can climb.

Some wind tunnel sections are larger than others because（　）

A:they are used for large planes B:they can produce a stronger wind C:they are built to conduct a high-speed test D:the air in them flows at a lower speed

A wind tunnel is used for testing planes or plane models. In a wind tunnel air is blown over a plane or a model placed in a test section. Wind tunnel test sections are different in size depending on airflow speed requirements. Some low-speed tunnels have test sections large enough for a complete small plane. In the very high speed tunnels used for space testing, however, the model may be as small as a pencil.
There are two ways of feeding air to the test section. In the constant flow tunnel, airflow produced by electric fans is forced through the tunnel to the test section, then through another tunnel section back to the starting point for reuse. The other way involves storing high-pressure air in a box, sending it out by a controlling device to pass through the tunnel and test section into another box. This way is usually used for a very short period of high-speed airflow.
Wind tunnels are usually used to test planes before they are flown. Problems in a plane can be found when it meets the high-speed airflow in the tunnel. For example, if the wings are built so that they would weaken at high speeds, this fact can be discovered in the tunnel, thus saving many lives and millions of dollars.
In a wind tunnel, scientists also find out how different planes will act at different speeds. They find out such things as how the air dives by the wing surfaces, how slowly a plane can fly before it starts to drop, and how fast it can climb.

What can we learn from the passage（　）

A:It is very expensive to build a wind tunnel. B:Wind tunnels are very essential in testing planes. C:Scientists still have a lot to learn about wind tunnels. D:There are new ways to feed air to the test section.

Passage Five A wind tunnel is used for testing planes or plane models. In a wind tunnel air is blown over a plane or a model placed in a test section. Wind tunnel test sections are different in size depending on airflow speed requirements. Some low-speed tunnels have test sections large enough for a complete small plane. In the very high speed tunnels used for space testing, however, the model may be as small as a pencil. There are two ways of feeding air to the test section. In the constant flow tunnel, airflow produced by electric fans is forced through the tunnel to the test section, then through another tunnel section back to the starting point for reuse. The other way involves storing high-pressure air in a box, sending it out by a controlling device to pass through the tunnel and test section into another box. This way is usually used for a very short period of high-speed airflow. Wind tunnels are usually used to test planes before they are flown. Problems in a plane can be found when it meets the high-speed airflow in the tunnel. For example, if the wings are built so that they would weaken at high speeds, this fact can be discovered in the tunnel, thus saving many lives and millions of dollars. In a wind tunnel, scientists also find out how different planes will act at different speeds. They find out such things as how the air dives by the wing surfaces, how slowly a plane can fly before it starts to drop, and how fast it can climb.Some wind tunnel sections are larger than others because ______.

A:they are used for large planes B:they can produce a stronger wind C:they are built to conduct a high-speed test D:the air in them flows at a lower speed

Passage Five A wind tunnel is used for testing planes or plane models. In a wind tunnel air is blown over a plane or a model placed in a test section. Wind tunnel test sections are different in size depending on airflow speed requirements. Some low-speed tunnels have test sections large enough for a complete small plane. In the very high speed tunnels used for space testing, however, the model may be as small as a pencil. There are two ways of feeding air to the test section. In the constant flow tunnel, airflow produced by electric fans is forced through the tunnel to the test section, then through another tunnel section back to the starting point for reuse. The other way involves storing high-pressure air in a box, sending it out by a controlling device to pass through the tunnel and test section into another box. This way is usually used for a very short period of high-speed airflow. Wind tunnels are usually used to test planes before they are flown. Problems in a plane can be found when it meets the high-speed airflow in the tunnel. For example, if the wings are built so that they would weaken at high speeds, this fact can be discovered in the tunnel, thus saving many lives and millions of dollars. In a wind tunnel, scientists also find out how different planes will act at different speeds. They find out such things as how the air dives by the wing surfaces, how slowly a plane can fly before it starts to drop, and how fast it can climb.As mentioned in the last paragraph, a wind tunnel can be used to find out ______.

A:how fast a plane can rise B:how smooth a plane’s surface is C:how a plane lands in a strong wind D:how a plane drops at a low height

Passage Five A wind tunnel is used for testing planes or plane models. In a wind tunnel air is blown over a plane or a model placed in a test section. Wind tunnel test sections are different in size depending on airflow speed requirements. Some low-speed tunnels have test sections large enough for a complete small plane. In the very high speed tunnels used for space testing, however, the model may be as small as a pencil. There are two ways of feeding air to the test section. In the constant flow tunnel, airflow produced by electric fans is forced through the tunnel to the test section, then through another tunnel section back to the starting point for reuse. The other way involves storing high-pressure air in a box, sending it out by a controlling device to pass through the tunnel and test section into another box. This way is usually used for a very short period of high-speed airflow. Wind tunnels are usually used to test planes before they are flown. Problems in a plane can be found when it meets the high-speed airflow in the tunnel. For example, if the wings are built so that they would weaken at high speeds, this fact can be discovered in the tunnel, thus saving many lives and millions of dollars. In a wind tunnel, scientists also find out how different planes will act at different speeds. They find out such things as how the air dives by the wing surfaces, how slowly a plane can fly before it starts to drop, and how fast it can climb.What can we learn from the passage

A:It is very expensive to build a wind tunnel. B:Wind tunnels are very essential in testing planes. C:Scientists still have a lot to learn about wind tunnels. D:There are new ways to feed air to the test section.

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{{B}}第一篇{{/B}}

One characteristic of weather maps not mentioned by the author in this passage is______.

A:wind speed B:thermal changes C:fronts D:barometric pressure