跟读练习: TOEFL Listening Practice #3 | Academic Lecture + Questions & Answers - 通过视频学习英语口语
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153 句
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You are about to listen to a TOEFL-style academic lecture.
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Listen carefully and take notes.
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You'll answer questions at the end.
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Let's begin.
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Alright, so last time we talked about some of the basic properties of stars.
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Temperature, brightness, distance.
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And today I want to start with a question that seems almost impossible to answer.
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What are stars made of?
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Now, think about the problem for a second.
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If a geologist wants to know what a rock is made of, what can she do?
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Take a sample?
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Exactly.
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Bring it into a laboratory, analyze it chemically.
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But obviously we can't do that with a star.
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Even the Sun is about 150 million kilometers away, and other stars are much, much farther.
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So how can astronomers say that a particular star contains hydrogen, helium, sodium, calcium, whatever?
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How can we know what's there without ever collecting a sample?
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The answer is light, more specifically something called spectroscopy.
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Now, you've probably seen what happens when white light passes through a prism.
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It makes a rainbow.
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Right.
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The light separates into different colors or different wavelengths.
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And if you do this carefully with light from a star, you get what we call a spectrum.
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But a stellar spectrum isn't usually just a smooth rainbow.
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There are dark lines at particular places in it.
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These are called absorption lines.
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And those little dark lines are enormously useful.
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In fact, you can think of them as… Well, almost like fingerprints. of the star?
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Not exactly of the star itself.
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Fingerprints of the chemical elements in the star's atmosphere.
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Let me explain.
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Every chemical element interacts with light in its own characteristic way.
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Hydrogen absorbs light at certain specific wavelengths.
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Sodium absorbs at another set of wavelengths.
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Calcium has its own pattern.
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So if astronomers see the characteristic absorption pattern of hydrogen in a star's spectrum, they know hydrogen is present.
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If they see the pattern associated with sodium, they know sodium is present.
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And so on.
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But how do they know which lines belong to which element in the first place?
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Good, that's the important part.
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We can determine that here on Earth.
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In a laboratory, scientists can heat different elements and examine the wavelengths of light associated with them.
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Each element produces a distinctive pattern.
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Then astronomers compare those laboratory patterns with the lines they observe in starlight.
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If the patterns match, they can identify the element, so we're not guessing what stars contain.
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We're comparing astronomical observations with measurements that can be reproduced in a laboratory.
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Now this idea became extremely important in the 19th century.
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And there's a nice historical example involving the Sun.
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Astronomers studying sunlight noticed a set of spectral lines that didn't match any element known at the time.
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So they proposed that there must be an element in the Sun that hadn't yet been discovered on Earth.
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Wait!
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They discovered an element in the Sun before they found it here?
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Exactly.
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That element was helium.
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The name actually comes from Helios, the Greek word associated with the Sun.
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Helium was identified in the solar spectrum before scientists confirmed its presence on Earth.
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And think about why that's significant.
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It demonstrated that spectroscopy could tell us about matter in a place we couldn't physically visit.
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That's a pretty remarkable idea.
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Now, I want to be careful here because there's an easy misunderstanding.
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When we look at a star's spectrum, we aren't necessarily seeing the composition of the entire star equally.
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Most of the absorption lines we observe are produced by material in the star's outer layers, its atmosphere.
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So we don't actually know what's inside the star?
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Well, that's going a little too far.
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We can learn about stellar interiors using other evidence and physical models.
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But spectroscopy gives us the most direct information about the material interacting with the light we observe, especially in the outer layers.
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So when you hear someone say, we know what the star is made of because of its spectrum, remember that there's a little more complexity behind that statement.
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Now, chemical composition isn't the only thing a spectrum can tell us.
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This is where it gets even more useful.
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Suppose I know exactly where a particular hydrogen line should appear.
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I look at a star, and the same line is there, but it's shifted slightly toward the red end of the spectrum.
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What might cause that?
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The star is cooler?
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can affect a spectrum, yes, but that's not what I'm describing here.
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If the whole pattern shifts toward longer, redder wavelengths, that can indicate that the star is moving away from us.
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And if the lines shift toward shorter, bluer wavelengths, it's moving toward us?
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Right?
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This is related to the Doppler effect.
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You've experienced the same basic phenomenon Imagine an ambulance approaching you with its siren on.
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The pitch sounds higher as it approaches and lower after it passes and moves away.
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With light, instead of hearing a change in pitch, we observe a change in wavelength.
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Movement away produces what we call a red shift.
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Movement toward us produces a blue shift.
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Now, don't take the ambulance analogy too literally.
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Sound waves and light waves aren't identical, and they don't travel in the same way.
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The analogy is useful because in both cases, relative motion affects the waves we observe.
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So from one spectrum you can tell what a star contains and whether it's moving?
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Yes, and potentially more than that.
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Spectra can provide information about temperature, density, rotation, magnetic fields.
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But for today I want you to remember the two basic ideas we've discussed.
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First, pattern of spectral lines can identify chemical elements.
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Second, shift.
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In the position of those lines can give us information about motion.
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Pattern tells us something about composition, shift tells us something about movement.
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Those are different pieces of information coming from the same starlight, and that's really the larger point.
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Astronomy often works this way.
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We can't touch most of the things we study, we can't bring a star into a laboratory, but the light reaching us carries information.
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The challenge is learning how to read it.
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Questions.
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1. What is the lecture mainly about?
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2. Why does the professor compare spectral lines to fingerprints?
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3. Why does the professor discuss the discovery of helium?
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4. Why does the professor say, well, that's going a little too far?
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5. According to the professor, what are two types of information that astronomers can obtain from spectral lines?
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6. What is the purpose of the professor's example of an ambulance siren?
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1. Correct answer.
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B. How astronomers use starlight to learn about stars.
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The lecture focuses on spectroscopy and the information astronomers can obtain by analyzing light from stars.
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The professor explains how spectral lines reveal chemical composition
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and how shifts in those lines can indicate whether a star is moving toward or away from Earth.
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Why the other answers are incorrect.
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A is incorrect because differences in stellar brightness are not the main subject.
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C is incorrect because laboratory experiments actually play an important role in identifying spectral patterns.
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D is incorrect because the lecture does not explain how astronomers calculate stellar distances.
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2. Correct answer.
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A. To emphasize that each chemical element has a distinctive spectral pattern.
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The professor explains that hydrogen, sodium, calcium, and other elements interact with light at specific wavelengths.
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Because each element has a characteristic pattern, Astronomers can compare the lines in starlight with patterns measured in laboratories.
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The fingerprint analogy emphasizes distinctive identification.
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The professor also immediately qualifies the analogy, the lines are not fingerprints of an individual star but of the chemical elements present in its atmosphere.
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3. Correct answer.
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C. To provide an example of spectroscopy revealing matter that had not yet been identified on Earth.
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Astronomers observed spectral lines in sunlight that did not match any element known at the time.
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They concluded that an unknown element must be present in the sun.
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That element was later identified as helium.
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The example demonstrates the power of spectroscopy.
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Scientists could identify evidence of a chemical element in a place they could not physically visit.
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4. Correct answer.
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A. The student has incorrectly concluded that astronomers know nothing about stellar interiors.
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The professor explains that absorption lines mainly provide direct information about material in a star's outer layers.
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The student then asks whether this means scientists do not know what is inside stars.
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The professor's response, that's going a little too far, signals that the student's conclusion is too strong.
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Astronomers can still learn about stellar interiors using other observations and physical models.
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This is a typical TOEFL speaker purpose flash function question.
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The professor is qualifying a student's interpretation rather than rejecting the original concept.
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5. Correct answers.
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A and C.
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The chemical composition of a star and the direction of a star's motion relative to Earth.
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The pattern of absorption lines can identify chemical elements.
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A shift in those lines can reveal relative motion.
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A red shift can indicate movement away from Earth, while a blue shift can indicate movement toward Earth.
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The professor summarizes this distinction near the end of the lecture.
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Pattern is composition.
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Shift is movement.
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6. Correct answer.
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C. To illustrate how relative motion can affect observed waves.
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The professor uses the familiar example of an ambulance siren to introduce the Doppler effect.
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As an ambulance approaches, its perceived pitch is higher.
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As it moves away, the pitch becomes lower.
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A related effect occurs with light.
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Instead of a change in perceived pitch, astronomers observe a change in wavelength.
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The professor also warns students not to take the analogy too literally because sound and light are different kinds of waves.
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The purpose of the example is therefore to make the general relationship between relative motion and observed waves easier to understand.
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本课的词汇与口语要点
这段视频共有 153 个句子、1628 个单词可供跟读。 讲话部分时长为 11:32。 说话人语速平稳，每分钟约 141 个词，很适合跟读。 只有 76% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中 15 个值得学习的单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| element 名词 | /ˈɛləmənt/ | 要素 |
| spectrum 名词 | /ˈspɛktɹəm/ | 範圍 /范围, 光譜 /光谱 |
| observe 动词 | /əbˈzɜːv/ | 遵守, 遵循 |
| laboratory 名词 | /ˈlæb(ə)ɹəˌtɔɹi/ | 實驗室 /实验室 |
| composition 名词 | /ˌkɑm.pəˈzɪʃ.ən/ | 成分 |
| hydrogen 名词 | /ˈhaɪdɹəd͡ʒ(ə)n/ | 氫 /氢 |
| stellar 形容词 | /ˈstɛl.əɹ/ | 优秀, 出色 |
| relative 名词 | /ˈɹɛl.ə.tɪv/ | 親戚 /亲戚 |
| lecture 名词 | /ˈlɛk.t͡ʃə/ | 演講 /演讲 |
| ambulance 名词 | /ˈæmbjᵿl(ə)n(t)s/ | 救護車 /救护车, 救生車 /救生车 |
| sodium 名词 | /ˈsəʊ.di.əm/ | 鈉 /钠 |
| analogy 名词 | /əˈnæləd͡ʒi/ | 類推 /类推, 類比 /类比 |
| absorption 名词 | /æbˈsɔɹp.ʃn̩/ | 吸收 |
| compare 动词 | /kəmˈpɛɚ/ | 比, 比較 /比较 |
| indicate 动词 | /ˈɪndɪˌkeɪt/ | 表明, 表示 |
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | is made · are called · can be reproduced |
| 现在完成时 have/has + 过去分词 — 过去发生但与现在仍有关联的事 | you've probably seen · You've experienced · we've discussed |
需要注意的发音
说话人用了 20 次缩略和弱读形式，例如 can't, don't, aren't。请按听到的简短形式来说。
- “th” 音: smooth /smuːð/, wavelength /ˈweɪvˌlɛŋ(k)θ/
- “sh” 和 “zh” 音: composition /ˌkɑm.pəˈzɪʃ.ən/, absorption /æbˈsɔɹp.ʃn̩/, associate /əˈsoʊʃi.ət/, observation /ˌɑbzɚˈveɪʃn̩/, flash /flæʃ/
- 长单词——注意重音位置: laboratory /ˈlæb(ə)ɹəˌtɔɹi/, composition /ˌkɑm.pəˈzɪʃ.ən/, analogy /əˈnæləd͡ʒi/, associate /əˈsoʊʃi.ət/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 用正常速度逐句跟读，每句重复到你的节奏与说话人一致为止。
- 录下自己的声音并与原声对比，特别注意 element, spectrum, observe 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。