2014年12月1日托福阅读真题+题目+答案：Forms of Locomotion
Using metabolic energy as “currency” to measure the “cost” of locomotion—that is, the amount of energy that must be spent to move from one place to another—we can compare the costs of different types of locomotion. Terrestrial locomotion—walking or running—is the most expensive form of locomotion. Given that humans are naturally terrestrial, many people may be surprised to learn that walking is so costly. The cost per kilogram of locomotion for human running is about five times higher than for the flight of a typical bird, and ten times more expensive than for fish swimming.
Just why is locomotion so cheap for a fish? The main reason is that the water supports most of the body weight of such a swimmer, so all the animal needs to do to swim is to produce enough force to overcome the drag of its own body. Most aquatic animals have nearly the same density as the water in which they swim, so they do almost no work to support their weight against gravity. However, swimming is cheap only for those animals well adapted to swimming completely submerged. When animals such as ducks and muskrat swim on the surface, they use two or three times more energy to swim on the surface than when submerged, and as much as twenty times more energy than fish of a similar size. This is because of what is called the “bow wave” any object moving on the surface of water pushes up a bow wave at the front, which streams alongside and trails back. Boat designers have long known that the bigger the bow wave, the harder it is to push a boat through the water. The bow wave produces extra drag on any body moving on the surface of water. An animal swimming on the surface of the water uses extra energy in order to overcome drag. Thus, for our purposes, efficient “swimming” means underwater locomotion by animals with streamlined bodies, not the exhausting, inefficient locomotion of humans in swimming pools.
Flying animals move through air that is less dense and less viscous than water, so why does flying cost more than swimming? First, most flying animals move much faster than a swimmer in order to produce enough lift (the upward force necessary to overcome gravity). This higher speed increases the drag that a flyer must overcome. Furthermore, a flyer has an extra source of drag that a swimmer does not have: the extra drag that comes from lift production. In a way, the extra drag represents the cost of supporting the flyer’s weight in air.
Walking (or running or galloping) is so costly because it involves at least three processes that require muscular work. The first is simply supporting the body’s weight. The second is overcoming the friction in joints and muscles, and the third is constantly producing accelerations (speeding up) and decelerations (slowing down). The exact proportion of muscular effort that goes into these three processes depends on the anatomy of a given animal, but the third process probably accounts for most of the energy used by the muscles. When a person takes a step, first one foot pushes off, which accelerates the body. Then the other foot swings forward and hits the ground, and as the weight shifts onto that foot, the body decelerates. Some of the leg muscles actively tense to act as shock absorbers during this deceleration. Momentum carries the body over the grounded foot, at which time that foot pushes off to accelerate the body, and the cycle repeats.
In terms of energy, walking is inefficient because of the acceleration and deceleration required with every step. Both the decelerations and accelerations need muscular effort and thus energy use. In swimming and flying, animals accelerate and decelerate relatively little over the course of a tail stroke or a wingbeat, so less energy is consumed by this process. As an analogy, consider riding a bicycle. When a person rides a bicycle, the bicycle does not accelerate or decelerate much with each turn of the petal. Thus, a person can ride a bicycle much faster than he or she could run using the same amount of effort.
1. According to paragraph 1, which of the following is true of the cost of locomotion?
A. For humans, the cost of running is lower than the cost of swimming.
B. The type of locomotion that comes most naturally to an animal is also the type of locomotion that is least expensive.
C. The more metabolic energy required for locomotion, the more expensive the locomotion is considered to be.
D. The faster a particular form of locomotion is, the more metabolic energy it requires.
2. Paragraph 2 suggests which of the following about the drag faced by aquatic animals?
A.The closer an aquatic animal’s body density is to the density of the water, the less drag the animal must overcome.
B. Aquatic animals that swim on the surface must overcome fewer sources of drag than animals that swim underwater.
C. The drag faced by most fish swimming underwater is much greater than previously thought.
D. All fish must overcome at least two forces of drag—the drag produced by their own bodies and by the bow wave.
3. According to paragraph 2, which of the following animal types is the most efficient swimmer?
A.Animals that are well suited to swimming completely submerged
B. Animals such as ducks and muskrat
C. Animals that spend their time both on the surface of the water and completely underwater
D. Animals that produce only a small bow wave
4. Select the TWO answer choices that, according to paragraph 2, are true of the swimming behavior of ducks and muskrat. To receive credit you must select TWO answer choices.
A.Ducks and muskrat require far more energy to swim on the surface than fish of a similar size require to swim underwater.
B Ducks and muskrat must overcome drag produced by the bow wave when swimming both on the surface and submerged.
C. Ducks and muskrat spend as much time underwater as possible in order to use less energy in swimming.
D. Ducks and muskrat are more efficient when swimming underwater than when swimming on the surface.
5. What is the author’s purpose in mentioning “Boat designers” in a discussion of the amount of energy used in swimming?
A.To illustrate the point that large animals are not efficient swimmers because they produce very large bow waves
B. To make a comparison between the type of drag produced by the bow wave and the type produced by an animal’s weight
C. To suggest that boat designers could design better boats if they studied locomotion in animals
D. To apply a principle used in boat design to further illustrate why surface swimming is inefficient
6. The word "exhausting" in the passage is closest in meaning to
C. extremely tiring
D. very complicated
7. The word "Furthermore" in the passage is closest in meaning to
B. In addition
8. According to paragraph 3, flying requires more energy than swimming for all of the following reasons EXCEPT: A flying animal must overcome more drag because it moves more quickly than a swimming animal. A flying animal must expend more energy to create lift than a swimming animal does. More energy is required for a flying animal to support its weight in air than for a swimming animal to support its weight in water. Because air has a lower density than water does, more energy is required for an animal to move through air than through water.
9. According to paragraph 4, which of the following statements is true about the energy expended by animals in walking?
A.It requires more energy for a walking animal to overcome the friction in its joints and muscles than to support its body weight.
B. The process involved in walking that usually requires the most energy is producing accelerations and decelerations.
C. Whether or not walking requires more energy than other types of locomotion depends on the anatomy of a given animal.
D. The energy generated by momentum during walking is greater than the amount of energy expended in accelerating and decelerating.
10. The word "consumed" in the passage is closest in meaning to
B. depended on
D. used up
11. Paragraph 5 states that swimming and flying are more efficient than walking because
A. swimming and flying animals make tail strokes and wingbeats much less often than walking animals take steps
B. swimming and flying animals use more muscles than walking animals do
C. swimming and flying do not require as much acceleration and deceleration with every movement
D.. animals that are swimming or flying can accelerate and decelerate more quickly than can animals that are walking
12. What is the author’s purpose in discussing “riding a bicycle”?
A. To explain why walking requires more energy than swimming and flying
B. To contrast the amount of energy used in riding a bicycle with the amount of energy used in swimming and flying
C. To suggest that humans should ride a bicycle instead of running or walking in order to conserve energy
D. To provide an example of an activity for which accelerations and decelerations require a great deal of muscular effort
Paragraph 3 Flying animals move through air that is less dense and less viscous than water, so why does flying cost more than swimming? First, most flying animals move much faster than a swimmer in order to produce enough lift (the upward force necessary to overcome gravity). ■This higher speed increases the drag that a flyer must overcome. ■Furthermore, a flyer has an extra source of drag that a swimmer does not have: the extra drag that comes from lift production. ■In a way, the extra drag represents the cost of supporting the flyer’s weight in air. ■
13. Look at the four squares [■] that indicate where the following sentence can be added to the passage.
Thus, the need to overcome resistance to fast forward motion plus the muscular effort needed just to keep from falling makes flying more energy intensive than swimming.
Where would the sentence best fit?
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Drag your choices to the spaces where they belong. To review the passage, click on View Text.
The amount of energy required for movement depends on the type of locomotion. ● ● ●
1.Swimming is cheaper than flying for animals that swim completely submerged but not for animals that swim on the surface of the water.
2.The demands of creating lift and overcoming drag make flying a more costly form of locomotion than swimming.
3.The costs of lift and drag are greater for walking and running than they are for swimming.
4.For animals that are well adapted to underwater swimming, locomotion requires very little energy because they do not have to support their own body weight.
5.Running and walking require more energy than other types of locomotion mainly because of the amount of muscular effort involved in constantly slowing the body down and speeding it up.
6.Riding a bicycle at a fast pace requires much less energy than either running or walking.