TPO
TPO7托福听力Lecture2原文文本
Narrator: Listen to part of a lecture in a Biology class.
Pro: So, that is how elephants use infrasound. Now, let’s talk about the other end of the acousticalspectrum, sound that is too high for humans to hear — ultrasound. Ultrasound is used by many animals that detect and some of them send out very high frequency sounds. So, what’s a good example? Yes? Carol.
Carol: Well, bats, since they are all blind, bats have to use sound for, you know, to keep from flying into things.
Pro: That’s echolocation. Echolocation is pretty self-explanatory; using echoes reflected sound waves to locate things. As Carol said, bats use it for navigation and orientation. And what else? Mike.
Mike: Well, finding food is always important, and I guess not becoming food for other animals.
Pro: Right, on both counts. Avoiding other predators, and locating prey, typically insects that fly around at night. Now before I go on, let me just respond to something Carol was saying— this idea that bats are blind. 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.
Ok, so quick summary of how echolocation works. The bat emits these ultrasonic pulses, very high pitch sound waves that we can’t hear. And then, they analyze the echoes, how the waves bounce back. Here, let me finish this diagram I started before class. So the bat sends out these pulses, very focused bursts of sound, and echoes bounce back. You know, I don’t think I need to draw on the echoes. Your reading assignment for the next class, it has a diagram that shows this very clearly.
So, anyway, as I were saying, by analyzing these echoes, the bat can determine, say, if there is wall in a cave that it needs to avoid, and how far away it is. Another thing it uses ultrasound to detect is the size and shape of objects. For example, one echo they quickly identify is the one they associatewith a moth, which is common prey for a bat, particularly a moth beating its wings.
However, moth happened to have a major advantage over most other insects. They can detectultrasound; this means that when a bat approaches, the moth can detect the bat’s presence. So, it has time to escape to safety, or else they can just remain motionless. Since, when they stop beating their wings, they’d be much harder for the bat to distinguish from, oh… a leaf or some other object.
Now, we have tended to underestimate just how sophisticated the abilities of animals that use ultrasound are. In fact, we kind of assumed that they were filtering a lot out, the way a sophisticatedradar system can ignore echoes from stationary objects on the ground. Radar does this to remove ground clutter, information about hills or buildings that it doesn’t need.
But bats, we thought they were filtering out this kind of information, because they simply couldn’t analyze it. But, it looks as if we were wrong. Recently there was this experiment with trees and a specific species of bats. A bat called: the lesser spear-nosed bat.
Now, a tree should be a huge acoustical challenge for a bat, right? I mean it’s got all kinds of surfaces with different shapes and angles. So, well, the echoes from a tree are going to a mass of chaotic acoustic reflections, right, not like the echo from a moth.
So, we thought for a long time that bats stop their evaluation at simply that is a tree. Yet, it turns out that bats or at least this particular species, cannot only tell that is a tree, but can also distinguish between, say, a pine tree, and a deciduous tree, like a maple or oak tree, just by their leaves. And when I say, leaves, I mean pine needles too. Any ideas on how it would know that?
Stu: Well, like with the moth, could it be their shape?
Pro: You are on the right track — It is actually the echo of all the leaves as whole that matters. Now, think, a pine tree with all those little densely packed needles. Those produce a large number of faint reflections in what’s... what’s called a ... a smooth echo.
The wave form is very even, but an oak which has fewer but bigger leaves with stronger reflections, produces a jagged wave form, or what we called: a rough echo. 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.
TPO7托福听力Lecture2题目文本
Question 1 of 6
What is the lecture mainly about?
A. How animals emit ultrasonic pulses.
B. How bats use acoustical signals.
C. A comparison of echolocation and radar.
D. Variations among bats in the use of ultrasound.
Question 2 of 6
Why does the professor decide NOT to add more information to the diagram on the board?
A. She wants students to complete the diagram themselves as an assignment.
B. She needs to look up some information in order to complete the diagram accurately.
C. The additional information is not relevant to the topic that she wants to discuss next.
D. Students already have the additional information in their textbook.
Question 3 of 6
According to the professor,what are two ways in which a moth might react when it detects the presence of a bat?Click on 2 answers.
A. The moth might stop beating its wings.
B. The moth might emit high-frequency sounds.
C. The moth might leave the area.
D. The moth might change its color to match its surroundings.
Question 4 of 6
What surprising information did a recent experiment reveal about lesser spear-nosed bats?
A. They filter out echoes from some types of trees.
B. They can analyze echoes from stationary objects with complex surfaces.
C. They cannot analyze "jagged" echoes.
D. They cannot analyze echoes from certain types of small moving objects..
Question 5 of 6
According to the professor ,why does a pine tree produce a "smooth" echo?
A. Because it has a smooth trunk.
B. Because it has large branches spaced at regular intervals.
C. Because it has many small,densely packed needles.
D. Because it remains stationary in all types of weather.
Question 6 of 6
playWhy does the professor say this?
A. To answer a question that Carol asked.
B. To correct a statement that Carol made
C. To praise Carol for an example that she gave
D. To give an example of a principle that Carol stated
TPO7托福听力Lecture2答案解析
Question 1 of 6
正确答案：B
题目解析：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。
Question2 of 6
正确答案：D
题目解析：教授提到You know, I don’t think I need to draw any echoes, your reading assignment for the next class; it has a diagram that shows this very clearly.说明相关图表在学生的教材中已经 出现，所以答案为 D。
Question 3 of 6
正确答案：AC
题目解析：教授提到the moth can detect the bat’s presence. So, it has time to escape to safety, or else they can just remain motionless.这句话讲出了moth发觉到蝙蝠的存在后的两种可能反映，一是逃走，二是保持静止。故应选A和C。
Question 4 of 6
正确答案：B
题目解析：本题的答案是 we thought for a long time that the bat stops their evaluation as simply that is a tree.这句话后面的内容。我们本来以为蝙蝠只能知道前面有棵树而不能分析得到进一步的 信息，但最近的研究显示蝙蝠可以通过树叶整体的形状分别出不同种类的树。所以B选项正确。
Question 5 of 6
正确答案：C
题目解析：这个问题应定位于原题中的 a pine tree with others’ little densely packed needles. Those produce a large number of faint reflections in which what’s called as: a smooth of echo.这一句。可以明确答案为C。
Question 6 of 6
正确答案：B
题目解析：Carol 曾经提到过蝙蝠都是盲的，而教授在这里想要纠正她这一说法。所以应选择B选项。
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