2020年11月22日托福阅读真题+题目+答案：Links between Echolocation and Flight

2020年11月22日托福阅读真题+题目+答案：Links between Echolocation and Flight

Echolocation, or sonar, means producing a sound that can be reflected back from solid objects and then listening for the echoes to sense where those objects are located. Microbats use their voices to produce ultrasonic sounds with high frequency (pitch). The wavelength of the sound determines the smallest object that will return an echo, and wavelength is inversely related to frequency: you need a very high frequency to get a short enough wavelength to detect small objects, say, the size of insects. Flight and echolocation in bats are linked by nocturnality (being active at night) and by a literal physical linkage between the wingbeat and call production. Bats are probably nocturnal because birds were already well established and diverse when bats were first evolving flight about 100 million years ago. The ancestors of bats were most likely already nocturnal and were able to evolve powered flight at night when birds are largely inactive. Some scientists have speculated that being nocturnal allowed bats to avoid competition with birds—although they would not have been competing for food because insect-catching birds did not evolve until much later. Other researchers have pointed out that the ancestral owls, hawks, and falcons were around when the bats first took to the air: so being nocturnal was probably important to avoid predators.

A small, nocturnal insect eater with sensitive hearing would have been able to detect and locate the movement noises of prey. This passive acoustic detection could have led to some form of echolocation: which would have been handy for getting around on really dark nights or detecting jumping or flying insects. It is not known whether the nonflying or the gliding ancestor of bats already used some form of echolocation or whether their descendants evolved it later; either way, it would have been a huge benefit to a nocturnal flyer. Many dark-adapted mammals rely on the sense of touch, particularly long whiskers: to find their way in total darkness. For a flyer moving rapidly through the air, whiskers would not have been much use for sensing obstacles in time to avoid them.

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1.According to paragraph 1, all of the following are true about echolocation in bats EXCEPT:

A It involves the production of sounds of high frequency. 

B It is used to locate small objects: such as insects.

C It is connected to flight in a number of ways.

D It allows bats to avoid competing with birds for food.

2.Paragraph 1 suggests which of the following about ancestral owls, hawks, and falcons?

A They were a threat to the ancestors of bats.

B They hunted primarily at night.

C They competed with ancestral bats for food.

D They evolved flight later than bats did.

3.According to paragraph 2, which of the following is likely true about the evolution of echolocation?

A Echolocation evolved before the ancestors of bats became nocturnal.

B Echolocation of some form evolved long before flying or gliding did.

C Echolocation evolved out of a very good sense of hearing.

D Echolocation evolved more rapidly in jumping or flying insects than it did in bats.

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