2018年12月16日托福阅读真题+题目+答案：Weak Electric Systems in Fish

2018年12月16日托福阅读真题+题目+答案：Weak Electric Systems in Fish

1. Some blind elephantnose fish produce weak electric signals that are used for detecting objects in their surroundingsa phenomenon called active electrolocation. These fish have specialized electric organs that discharge either in pulses or in a wave-like fashion, depending on the species. Although discharges follow one another almost continuously throughout the life of the fish, their power level is much too low to be detected by human handlers but potent enough to create a stable electric field around the body of the fish. When an object enters into this electric field, it causes distortions in the current that are detected by electroreceptor organs distributed over the fish's skin.

2. A weak electric system may have several uses, including the exploration of novel environments. For example, blind elephantnose fish can easily find the only opening that allows them to cross through a newly installed partition within their aquarium, even though they cannot see it with their eyes. Their electric sense must be implicated because when these individuals become electrically silent (unable to use their electric system through denervation of their electric organs), they can no longer find the opening.

3. During the 1970s, biologists became interested in the role of the weak electric system not only as a means of electrolocation but also as a means of electrical communication between individual fish. Communication is possible because the rate and waveform of the electric discharges can vary between species, between sexes, between individuals, or even between situations in the same individual. Moreover, some fish can temporarily interrupt their normally continuous train of discharges, and these pauses can be full of meaning. The effective range of communication by electric signals can reach a little over 1 meter depending on water resistance.

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托福阅读真题题目：

1..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. Throughout the life of the fish, its electric discharges vary in power from undetectable to fairly potent.

B. Nearly continuous discharges undetectable by humans create a stable, low-level electric field around the body of the fish.

C. Human handlers cannot feel the electric discharges because the discharges are at such low power levels.

D. The discharges are so weak that they would have to be fired almost continuously to create a detectable electric field.

2..The word distortions in the passage is closest in meaning to

A. decreases

B. signals

C. concentrations

D. irregularities

3..Paragraph 2 describes an experiment with elephantnose fish that were electrically silent and therefore unable to

A. distinguish between new and familiar objects in their aquarium

B. swim around the partition in their aquarium

C. find their way through a hole in a barrier

D. see with their eyes

4..All of the following are mentioned in paragraph 3 as components of communication in electric fish EXCEPT

A. the rate of electric discharges

B. the direction in which discharges travel

C. the waveform of electric discharges

D. pauses between electric discharges

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