2015年9月12日托福阅读真题+题目+答案：Gliding and Soaring
1. Gliding is gravity-powered flight where the movement of the glider has a downward tilt. But many birds are capable of ascending without flapping their wings, and this is called
soaring.Birds usually soar by finding air that is rising as fast as or faster than the gliding bird's sinking speed. For example, a turkey vulture might glide with a sinking speed of about 0.8 meters per second. If the vulture can find a place where the air is rising at 0.8 meters per second, it will be able to maintain a constant altitude. If it finds air rising faster than that, it will be able to climb.
2. Two common processes produce updrafts, or rising air. When heated air rises, it is called a thermal, and when wind blows up a hill or over a large obstacle, it is called ridge lift or slope lift. Thermals occur when the Sun heats some parts of the ground more than others. For example, a freshly plowed field may heat up faster than an adjacent meadow. The warm ground heats the air above it, and the air starts to rise. As the warm air rises, it is replaced by cool air from the surrounding terrain, and this new air is heated until it rises. Thermals may be continuous chimneys of rising air, or a series of discrete, doughnut-shaped bubbles (ring thermals) formed at intervals by the warmed ground.
3. If they could be made visible, ring thermals would look like giant, rising smoke rings. Some airplane pilots and biologists disagree about the exact form of continuous thermal chimneys. Pilots have traditionally interpreted thermals as large, tall columns of rising air, usually with a cumulus (white, fluffy) cloud marking the top of the column. In contrast, observers of animal flight find only small, localized thermal chimneys, which usually take the form of dust devils, which are small columnar thermals with intense rotation. Colin Pennycuick, a prolific researcher on bird flight, discounts thermal chimneys and recognizes only ring thermals as sources of large-scale, long-lasting updrafts. In any case, thermals can rise 2 or 3 kilometers above the ground. Also, they tend to increase in size and intensity as they rise, sometimes reaching over 1,000 meters in diameter. Thermals are usually capped by a cloud, because the upper limit of a thermal is set by the altitude where the temperature is low enough to condense water vapor in the thermal, which cools the air and forms a cloud.
4. As long as the upward speed of the thermal is greater than the sinking speed of a glider, the glider will ascend in the thermal. Of course, the glider will quickly fly out of the thermal if it flies in a straight line, so it must circle to stay in the rising air. (A glider should stay on the inside of the ring, because the air on the outer edge of the ring is actually rolling downward.) Imagine a vulture ascending to 1,500 meters above the ground by circling in a ring thermal. From this height, it will be able to fly out of the thermal and glide for about 30 minutes (traveling over 23 kilometers) before it runs out of altitude and needs to either start flapping, find another thermal, or land. Many soaring birds use just this pattern: climbing up in a thermal, gliding a long distance, then finding another thermal in which to soar. This type of flight is an efficient way to cover long distances at a low energy cost, making it a handy way to migrate or search for food.
5. Slope soaring is useful when wind blows upward along a slope. The speed of the wind's upward motion can be calculated in the same manner that the sinking speed of a glider is calculated. If the upward speed of this wind is greater than or equal to the sinking speed of a glider, the glider will be able to maintain altitude. Such ridge lift has a characteristic that is both an advantage and a disadvantage: ridge lift is usually predictably tied to a particular slope, so it is easy to find. But it is usable only in that fixed, local area.
1..Which of the following plays a role in helping a bird to soar
B. Wing flapping
D. Rising air
2..In paragraph 1, why does the author discuss the example of a turkey vulture in flight
A. To explain why birds sink unless they find currents of rising air
B. To provide information about sinking and soaring speeds typical for large birds
C. To illustrate why gliding birds seek out rapidly rising air currents
D. To clarify the relationship between sinking speed and the speed of rising air needed to soar
3..The word adjacent in the passage is closest in meaning to
C. densely covered
4..The phrase at intervals in the passage is closest in meaning to
A. at low elevations
B. in areas without vegetation
5..The word discrete in the passage is closest in meaning to
6..Paragraph 2 implies that which of the following is a factor that contributes to the formation of thermals
A. In some areas, characteristics of the ground cause it to heat more than surrounding areas.
B. The sun heats the air, causing it to start to rise.
C. Warm air continues to rise until the ground beneath it is cooled by colder air.
D. Uneven heating of the air causes it to rotate as it rises.
7..The word prolific in the passage is closest in meaning to
C. highly productive
D. highly respected
8..Which of the sentences below best expresses the essential information in the highlighted sentence in the passage Incorrect choices change the meaning in important ways or leave out essential information.
A. Thermals capped by clouds have upper limits when the temperature gets low enough to condense water vapor.
B. Thermals usually stop rising when they reach a cloud, because thermals are limited in the amount of water vapor they can hold before the vapor condenses.
C. Most thermals have clouds at their upper end, because thermals stop rising in places cool enough to condense the thermal's water vapor.
D. Thermals usually rise to the same altitude as clouds, because cool air in clouds allows the water vapor to condense.
9..Which TWO statements below about thermal chimneys would the biologists discussed in paragraph 3 regard as likely true To receive credit, you must select TWO answers.
A. They cover only a small area.
B. They sometimes contain dust devils.
C. They usually spin very quickly.
D. They usually end in a fluffy cloud.
10..Paragraph 3 indicates that all of the following are true of thermals EXCEPT:
A. Air movement is more intense at their higher reaches.
B. They can rise above cloud level.
C. They usually become wider as they rise.
D. They sometimes rise more than a kilometer from Earth's surface.
11..According to paragraph 4, a bird that flies by alternating between soaring and gliding gains which of the following advantages
A. It can often cover short distances faster than it could by flapping its wings to travel.
B. It is able to travel a long way without using a lot of energy.
C. It can find thermals more quickly than it could by flapping its wings to travel.
D. It can stay inside the thermal regardless of how thermal speeds change.
12..Which of the following is discussed in paragraph 5 as a disadvantage of slope soaring as compared to thermal soaring
A. Slope soaring does not allow a bird to remain at a constant altitude.
B. Gliders tend to travel at slower speeds during slope soaring than during thermal soaring.
C. Slope soaring is limited to the area where the particular slope is located.
D. It is difficult to predict the location of an area suitable for slope soaring.
13..Look at the four squares that indicate where the following sentence could be added to the passage.
Soaring uses energy such as rising air currents to allow birds to increase time aloft.
Where would the sentence best fit Click on a square to add the sentence to the passage.
14..Drag your choices to the spaces where they belong. To review the passage, click on View Text .
A. Birds can soar by finding an updraft, which is created either by air rising from ground that is warmer than the surrounding ground or by wind blowing up a hill or over a large obstacle.
B. Soaring is possible in updrafts in which the air's upward speed is greater than the bird's sinking speed.
C. Birds flying over a flat meadow often need to flap their wings in order to stay at the same altitude because thermal chimneys and ring thermals typically do not form in such areas.
D. Birds can travel in an energy-efficient way by soaring upward in thermals and then leaving the thermal and gliding to lower altitudes.
E. Birds that need to fly over long distances generally do not use thermals because they limit the distance the birds can soar.
F. Thermals that form as a result of ridges have predictable speeds that depend on the incline of the particular slope and the climate of the local area.