Dolphin's navigation托福聽力原文翻譯及問題答案

Dolphin's navigation托福聽力原文翻譯及問題答案

一、Dolphin's navigation托福聽力原文：

NARRATOR:Listen to part of a lecture in a marine biology class.

FEMALE PROFESSOR:We have been talking about how sea animals find their way underwater,how they navigate,and this brings up an interesting puzzle,and one I'm sure you'll all enjoy.I mean,everybody loves dolphins,right?

And dolphins—well,they actually produce two types of sounds,um,one being the vocalizations you're probably all familiar with,which they emit through their blowholes.But the one we're concerned with today is the rapid clicks that they use for echolocation,so they can sense what is around them—these sounds,it's been found,are produced in the air-filled nasal sacs of the dolphin.

And the puzzle is:How do the click sounds get transmitted into water?It's not as easy as it might seem?You see,the denser the medium,the faster sound travels.So sound travels faster through water than it does through air. So what happens when a sound wave?um,okay,

you've got a sound wave traveling merrily along through one medium,when suddenly it hits a different medium.What's gonna happen then?Well,some of the energy is gonna be reflected back,and some of it's gonna be transmitted into the second medium.

An-an-and if the two media have really different densities—like air and water—then most of the energy is gonna be reflected back;very little of it will keep going—uh,get transmitted into the new medium.I mean,just think how little noise from the outside world actually reaches you when your head's underwater.So,how do the dolphin's clicks get transmitted from its air-filled nasal sacs into the ocean water? Because given the difference in density between the air in the nasal cavity and the seawater,we'd expect those sounds to just kinda go bouncing around inside the dolphin's head!Which would do it no good at all?if it's going to navigate,it needs those sounds to be broadcast and bounce back from objects in its path.

Well,turns out dolphins have a structure in their foreheads,just in front of their nasal sacs,called a melon.Now the melon is kind of a large sac-like pouch made up of fat tissue.And this fat tissue has some rather fascinating acoustical properties. Most of the fat that you find in an animal's body is used for storing energy,but this fat—what you find in dolphins,and only in the melon and around the lower jaw—this fat is very different,very rich in oil—and it turns out it has a very different purpose as well.

Now,one way to overcome this mismatch in the density of air and water would be? if you could,um,modify the velocity of the sound wave,make it precisely match the speed at which sound travels through water. And that's exactly what marine biologists have discovered the melon does.Note that the bursae,these little projections at the rear of the melon,are right up against the air-filled nasal sacs—and these bursae,it turns out,are what's responsible for transferring sound to the melon.

The sound waves are transmitted by the bursae through the melon—first through a low-velocity core,and then through a high-velocity shell,where their speed is increased before they are transmitted into the surrounding seawater.So now the signals can be efficiently transferred into the water,with minimal reflection.The only other place this special fatty tissue—like that in the melon—the only other place it's found in the dolphin is in the lower jaw. Turns out that the lower jaw—well,it's made of especially thin bone, and it's very sensitive to vibrations,to sound energy traveling through the seawater.It turns out that the jaw is primarily responsible for capturing and transferring returning sound waves to the dolphin's inner ear.

So,these rapid clicks that are sent out bounce off objects—m-maybe a group of fish swimming over here,a boat coming from over there—the sounds bounce off them and the lower jaw captures the returning sounds,making it possible for the dolphin to sense what's in the surrounding water and decide where to swim.

二、Dolphin's navigation托福聽力中文翻譯：

旁白：在海洋生物課上聽一節(jié)課的一部分。

女教授：我們一直在討論海洋動物如何在水下找到它們的路，它們?nèi)绾螌?dǎo)航，這帶來了一個(gè)有趣的謎題，我相信你們都會喜歡的。我是說，每個(gè)人都喜歡海豚，對嗎？

海豚實(shí)際上會發(fā)出兩種聲音，一種是你們可能都熟悉的聲音，它們通過氣孔發(fā)出。但我們今天所關(guān)心的是它們用來進(jìn)行回聲定位的快速咔噠聲，這樣它們就可以感知周圍的東西。我們發(fā)現(xiàn)，這些聲音是在海豚充滿空氣的鼻囊中產(chǎn)生的。

難題是：咔噠聲是如何傳播到水中的？這不像看起來那么容易？你看，介質(zhì)密度越大，聲音傳播的速度越快。所以聲音在水中傳播的速度比在空氣中傳播的速度快&nbsp；那么當(dāng)聲波出現(xiàn)時(shí)會發(fā)生什么呢？嗯好吧，

聲波在一種介質(zhì)中歡快地傳播，突然它碰到另一種介質(zhì)。那會發(fā)生什么？一些能量會被反射回來，一些能量會被傳輸?shù)降诙N介質(zhì)中。

如果這兩種介質(zhì)的密度真的不同，比如空氣和水，那么大部分能量都會反射回來；只有很少一部分會繼續(xù)傳播到新媒體中。我的意思是，想想看，當(dāng)你的頭在水下時(shí)，外界發(fā)出的噪音是多么的小。那么，海豚的咔噠聲是如何從充滿空氣的鼻囊傳播到海水中的呢；因?yàn)榭紤]到鼻腔中的空氣和海水的密度不同，我們預(yù)計(jì)這些聲音會在海豚的腦袋里彈來彈去！那根本沒用？如果要導(dǎo)航，它需要廣播這些聲音，并從其路徑中的對象中反彈回來。

海豚的額頭上有一個(gè)結(jié)構(gòu)，就在鼻囊的前面，叫做瓜?，F(xiàn)在甜瓜是一種由脂肪組織組成的大的囊狀袋。這種脂肪組織有一些非常迷人的聲學(xué)特性&nbsp；你在動物體內(nèi)發(fā)現(xiàn)的大部分脂肪都是用來儲存能量的，但這種脂肪與你在海豚體內(nèi)發(fā)現(xiàn)的脂肪非常不同，只有在瓜和下頜周圍，這種脂肪非常富含油脂，結(jié)果證明它也有非常不同的用途。

現(xiàn)在，克服空氣和水密度不匹配的一種方法是；如果你能，嗯，修改聲波的速度，使其與聲音在水中傳播的速度精確匹配；這正是海洋生物學(xué)家發(fā)現(xiàn)甜瓜的作用。請注意，耳囊，即甜瓜后部的這些小突起，正對著充滿空氣的鼻囊，而這些耳囊，事實(shí)證明，是負(fù)責(zé)將聲音傳遞給甜瓜的。

聲波由囊通過瓜傳播，首先通過一個(gè)低速的核心，然后通過一個(gè)高速的外殼，在那里它們的速度增加，然后再傳播到周圍的海水中。因此，現(xiàn)在信號可以有效地傳輸?shù)剿?，反射最小。這種特殊的脂肪組織，像甜瓜中的脂肪組織，在海豚身上發(fā)現(xiàn)的唯一其他地方是下頜；事實(shí)證明，下顎是由特別薄的骨頭組成的；它對振動非常敏感，對穿過海水的聲能非常敏感。結(jié)果表明，下巴主要負(fù)責(zé)捕捉并將返回的聲波傳輸?shù)胶ｋ嗟膬?nèi)耳。

因此，這些發(fā)出的快速咔噠聲會從物體上反彈——m——可能是一群魚在這里游泳，一艘船從那里駛來——聲音會從物體上反彈回來，而下頜骨會捕捉到返回的聲音，使海豚能夠感知周圍水里的東西，并決定在哪里游泳。

三、Dolphin's navigation托福聽力問題：

Q1:1.What is the lecture mainly about?

A.Parts of the dolphin's anatomy that allow it to navigate.

B.Two different types of communication used by dolphins.

C.The way that dolphins store air while swimming underwater.

D.The meanings of different signals used by dolphins.

Q2:2.Why does the professor discuss the speed at which sound travels?

A.To describe why sounds made under water can travel long distances

B.To show why a person cannot hear a dolphin well when it is under water

C.To compare the speed of two different sounds made by dolphins

D.To explain how sound waves behave when crossing from one medium into another

Q3:3.What is the dolphin's melon?

A.An oval-shaped bone that lets the dolphin hear sounds

B.An organ made of fat tissue that helps a dolphin send sound waves

C.An air-filled cavity that lets the dolphin breathe underwater

D.An organ filled with water that helps the dolphin measure depth

Q4:4.What is the dolphin's jaw able to do?

A.Send rapid clicking sounds into water

B.Increase the speed of sounds

C.Receive sound waves that have reflected off objects

D.Force water through the nasal sacs and out the blowhole

Q5:5.How does the professor organize the information in the lecture?

A.By describing a phenomenon and the physical structures that make it possible

B.By describing several of the dolphin's senses and their relative usefulness

C.By contrasting how the dolphin makes two different types of sounds

D.By describing an old theory and then a new theory

Q6:6.Why does the professor say this:

A.To find out whether students are familiar with the lecture topic.

B.To mention a related topic that will not be discussed in detail.

C.To mention a common misconception about dolphin vocalizations.

D.To point out a primary function of dolphin blowholes.

四、Dolphin's navigation托福聽力答案：

A1:正確答案：A

A2:正確答案：D

A3:正確答案：B

A4:正確答案：C

A5:正確答案：A

A6:正確答案：B

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