您IP所在的地区,暂不支持官方真题素材

建议使用其他功能进行听力练习

返回
小站备考
托福
托福听力
Official7听力真题

托福official7听力lecture2 Bats' Use of Ultrasound原文解析+翻译音频

展开
Tip:单击查看句义;划选/双击查生词

[00:00.00]Narrator: Listen to part of a lecture in a biology class.
[00:06.36]FEMALE PROFESSOR: So, that’s how elephants use infrasound… [00:09.80]Now let's talk about the other end of the acoustical spectrum—sound that's too high for humans to hear: ultrasound. [00:18.47]Ultrasound is used by many animals that detect—and, some of them, send out—very high-frequency sounds. [00:27.82]So, what's a good example?[00:30.47]Yes, Carol?
[00:31.88]FEMALE STUDENT: Well, bats—since they're all blind, bats have to use sound for—uh, y'know—to keep from flying into things.
[00:41.69]FEMALE PROFESSOR: That’s echolocation. [00:45.24]Echolocation is pretty self-explanatory: Using echoes—reflected sound waves—to locate things… [00:55.10]As Carol said, bats use it for navigation and orientation… [00:59.53]and what else? Mike?
[01:03.60]MALE STUDENT: Well, finding food is always important—and, uh, I guess, not becoming food for other animals…
[01:12.33]FEMALE PROFESSOR: Right on both counts. [01:14.19]Avoiding other predators—and locating prey—uh, typically insects that fly around at night.  [01:21.19]Now, before I go on, let me just respond to something Carol was saying—this idea that bats are blind… [01:27.93]actually, there are some species of bats—the ones that don't use echolocation—that do rely on their vision for navigation but, it is true that, for many bats, their vision is too weak to count on.
[01:41.56]OK, so: quick summary of how echolocation works. [01:46.68]The bat emits these ultrasonic pulses—very high-pitched sound waves that we can't hear—[01:52.85]and then: they analyze the echoes—how the waves bounce back. [01:57.86]Uh, here, let me finish this diagram I started before class…[02:01.99]So the bat sends out these pulses—very focused bursts of sound, and echoes bounce back…  [02:12.47]Y'know, I don't think I need to draw in the echoes. [02:18.66]Your-your reading assignment for the next class—it has a diagram that shows this very clearly—
[02:22.96]so anyway as I was saying… By analyzing these echoes, the bat can determine, say, if there's a wall in a cave that it needs to avoid… and—how far away it is. [02:35.77]Another thing it uses ultrasound to detect, is the size and shape of objects. [02:41.49]For example, one echo they’d quickly identify is the one they associate with a moth, which is common prey for a bat—particularly, a moth beating its wings.
[02:51.15]However, moths happen to have a major advantage over most other insects: [02:56.01]they can detect ultrasound. This means that, when a bat approaches, the moth can detect the bat's presence… [03:03.85]so it has time to escape to safety… or else they can just remain motionless—[03:09.44]since, um, when they stop beating their wings, they’d be much harder for the bat to distinguish from, oh, a-a leaf… or-or some other object… 
[03:18.90]Now, we've tended to underestimate just how sophisticated the abilities of animals that use ultrasound are. [03:26.16]In fact, we kind of assumed that they were filtering a lot out—uh, the way a sophisticated radar system can ignore echoes from stationary objects on the ground. [03:37.08]Radar does this to remove “ground clutter”—information about, um, hills or buildings that it doesn’t need.
[03:44.76]But bats—we thought they were filtering out this kind of information because they simply couldn't analyze it. [03:51.81]But it looks as if we were wrong. [03:54.40]Recently, there was this experiment with trees and a specific species of bats—[04:00.46]a bat called the lesser spear-nosed bat.
[04:03.90]Now a tree should be a huge acoustical challenge for a bat, right? [04:09.61]I mean, it's got all kinds of surfaces, with different shapes and angles… [04:14.28]So, well, the echoes from a tree are going to be a mass of chaotic acoustic reflections, right? Not like the echo from a moth.
[04:23.26]So, we thought, for a long time, that bats stopped their evaluation at simply “that's a tree.” [04:30.63]Yet, it turns out that-that bats, or at least this particular species, can not only tell that it’s a tree, but can also distinguish between, say, a pine tree and a deciduous tree—like, a maple, or an oak tree: just by their leaves—[04:47.24]an-and when I say “leaves,” I mean pine needles, too. [04:50.85]Any ideas on how it would know that?
[04:54.50]MALE STUDENT: Well… like with the moth—could it be their shape?
[05:02.05]FEMALE PROFESSOR: You're on the right track. It’s actually the echo off all the leaves—as a whole—that matters. [05:09.05]Now, think: A pine tree—with all those little, densely packed needles… [05:15.19]those produce a large number of faint reflections in wh-what's called a-a “smooth” echo—
[05:21.12]the waveform is very even … but an oak—which has fewer but bigger leaves with stronger reflections—produces a jagged waveform—or what we call a “rough” echo. [05:34.03]And these bats can distinguish between the two—and not just with trees, but with any echo that comes in a smooth or rough shape.

1.What is the lecture mainly about?

你的答案:
正确答案:B
题目解析:
 后才能查看题目解析,还没有账号? 马上注册
主旨题。Lecture 的主要内容是讲述蝙蝠如何利用超声波进行定位、避险、捕食等行为。答案应为 B。Lecture并没有讲诉动物发出超声波的机理,所以A选项错误;讲座中有 提到雷达和 echolocation 的比较,但并不是讲座主线,所以C选项错误;讲座中有提及有些蝙蝠可以靠视力定位,而大多数蝙蝠只能靠超声波,但这部分内容不算讲座的主线,所以 D 选项错误。

学习页面

Medi

terr

anean

加强 + 政府 + 名词后缀

加强的政府——管理

原文例句

加入生词

本文生词 0

色块区域是你收藏过的生词;

查询次数越多,颜色越深哦~

显示文中生词

登录后才能收藏生词哦,现在登录注册>

本文重点词 45

文中加粗单词为本文重点词;

根据词频与核心词范围精心挑选,托福考试必掌握词汇。

显示文中重点词
学习本文词汇

文中划选/双击的生词、加粗重点词已收纳至词盒

可随时点击词盒查看哦~

只有在词句精学模式下才能开启词盒功能哦~

我知道了

词盒
收藏
笔记
我的笔记
5000
保存
反馈