2021年9月18日 托福阅读真题+题目+答案：Echolocation in Bats

2021年9月18日 托福阅读真题+题目+答案：Echolocation in Bats

In a process known as echolocation,some animals use reflected sound waves to assess their surroundings.Echolocation has been best studied in bats.Today the general consensus among scientists is that the functions of bat echolocation are primarily to acquire food (for example,flying insects)and secondarily to orient in darkness. Echolocation and other sounds are measured in frequency (vibrations per second),using a unit of measure called a hertz (Hz).Sounds emitted by bats can range between 100 and 200,000 Hz,but those used for echolocation are generally between 25,000 and 140,000 Hz. Because humans typically hear sounds between about 20 and 20,000 Hz,echolocation in bats is truly ultrasonic from a human standpoint.

1.The word “assess"in the passage is closest in meaning to

O control

O evaluate

O adapt to

O communicate about

2.Paragraph 1 suggests which of the following about sounds emitted by bats?

O They can be used for purposes other than echolocation.

O They are limited to a narrower range of frequencies than the sounds made by humans.

O They have never been measured at frequencies below 100,000Hz.

O They are not emitted outside the bat's own territory.

Why are ultrasonic signals produced by bats so high in frequency? Bats almost certainly did not evolve ultrasounds in order to fly undetected by humans and other potential predators;instead, evolution probably had a lot to do with prey capture and navigation.A bat flying at 30 kilometers per hour in relative darkness is able to detect and capture flying insects several meters away that are about eleven millimeters or smaller.Under these circumstances,a rapid series of signals of about 30,000 Hz allows the bat to produce wavelengths eleven millimeters in size that match the body size of an eleven-millimeter flying insect.When the wavelength of the signals emitted by a bat is the same as that of the intended prey,a better echo returns to the bat,thereby giving the bat more precise information on the location of the prey.The detection of insects smaller than eleven millimeters would require bats to emit signals even higher than 30,000 Hz in frequency.

3.The word “precise"in the passage is closest in meaning to

O exact

O useful

O reliable

O comprehensive

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