2018年8月25日托福阅读真题+题目+答案：Forms of Locomotion

2018年8月25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.

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.

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.

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

A.enjoyable

B.corresponding

C.extremely tiring

D.very complicated

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.

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