托福考试是学术英语考试 academic English，考察目的是检验考生是否具备在国外大学里学习的能力，具体说就是你能听懂课吗?你会跟学校各种工作人员正常沟通吗?因此听力只考察两类内容：两篇课下对话 conversation 和四篇课堂讲课 lecture 。Lecture 就是浓缩的一堂大学讲课，内容几乎涵盖了大学里所能涉及到的所有基础性科目，生命科学，艺术文学，社会科学，自然科学等。每篇 lecture 时长在五分钟左右，后面紧跟六个问题，多数为单选题，也会有多选题，重听题，排序题等。同学们对 lecture 的总结是：题目多难度大，一堂充满深深恶意的老师讲课。
攻克 lecture我们需要认真思考的一大问题就是 —— lecture 结构特点是什么?换言之就是老师最喜欢怎么展开一堂课?
原 文 解 析
我们以 TPO17 Lecture4 为例：(以下内容仅限于听完 TPO17 Lecture4 的同学阅读，所以.....还不赶紧去听!!!)
Ok, now I want to talk about an animal that has a fascinating set of defense mechanisms. And that’s the octopus, one of the unusual creatures that live in the sea. The octopus is prey to many species, including humans, so how does it escape its predators?
Well, let me back up here a second. Anyone ever heard of Proteous? Proteus was a God in Greek mythology who could change form. He could make himself look like a lion or a stone or a tree, anything you wanted, and he could go through a whole series of changes very quickly. Well, the octopus is the real world version of Proteus. Just like Proteus, the octopus can go through all kinds of incredible transformations. And it does this in three ways: by changing color, by changing its texture, and by changing its size and shape.
围绕专有名词 Proteus 展开，重点强调了 Proteus 具有 change form, transform 的能力。
For me, the most fascinating transformation is when it changes its color. It’s a normal skin color, the one it generally presents, is either red or brown or even grey, and it ’s speckled with dark spots. But when it wants to blend in with its environment to hide from its enemies, it can take on the color of its immediate surroundings: the ocean floor, a rock, a piece of coral, whatever. Charles?
Student：Do we know how that works, I mean, how they change colors?
Professor ：Well, we know that the reaction that takes place is not chemical in nature. The color changes are executed by two different kinds of cells in the octopus ’ skin, mainly by color cells on the skin’s surface called chromatophores. Chromatophores consist of tiny sacks filled with color dye. There might be a couple hundred of these color sacks per square millimeter of the octopus ’ skin, and depending on the species, they can come in as many as five different colors. Each one of these sacks is controlled by muscles. If the muscles are relaxed, the sack shrinks, and all you see is a little white point. But if the muscle’s contract, then the sack expands, and you can see the colors. And by expanding different combinations.
Student: And just with various combinations of those five colors, they can recreate any color in their environment?
Professor: Well, they can no doubt create a lot with just those five colors, but you are right, maybe they can’t mimic every color around them, so that’s where the second kind of cell comes in. Just below the chromatophores is a layer of cells that reflect light from the environment, and these cells help the octopus create a precise match with the colors that surround them. The colors from the color sacks are supplemented with colors that are reflected from the environment, and that ’s how they are able to mimic colors with such precision. So, that’s how octopus mimic colors.
分论点二讲解 how to change color，重点强调了两种细胞，一种叫做 chromatophores ,这种细胞 controlled by muscles . 另外一种细胞能够 reflect light.
But they don’t just mimic the colors in their environment; they can alos mimic the texture of objects in their environment. They have these little projections on their skin that allow them to resemble various textures. The projections are called papillae. If the octopus wants to have a rough texture, it raises the papillae. If it wants to have a smooth texture, it flattens out the papillae, so it can acquire a smooth texture to blend in with the sandy bottom of the sea. So the octopus has the ability to mimic both the color and the texture of its environment. And it’s truly amazing how well it can blend in with its surroundings. You can easily swim within a few feet of an octopus and never see it.
分论点三讲解 how to change texture , 引入专有名词 Papillae。
Um, now there’s a third way that octopus can transform themselves to blend in with or mimic their environment, and that’s by changing their shape and size, well, at least their apparent size. The muscular system of the octopus enables it to be very flexible to assume all sorts of shapes and postures. So it can contract into the shape of a little round stone, and sit perfectly still on the seafloor. Or it can nestle up in the middle of a plant and take the shape of one of the leaves.Even Proteus would be impressed, I think.
分论点四讲解 how to change size and shape, 举了 stone 和 leaves 的两个例子，文章结束。
Topic: animal, octopus, escape predators
Subtopic1: Proteus: change form, transform
Subtopic2: color:chromatophores, controlled by muscles
Subtopic4: shape&size:eg. stone, leaves
为什么掌握 lecture 的结构特点如此重要?这是由 lecture 的题目设置特点决定的。
第一：考察大结构和重点强调内容，不考小细节。 Lecture 的结构特点很明确的展示出重点内容的出现位置：开篇点题处，每个段落的主题句(一般是段落的第一句话)，课堂总结处。翻译一下就是，这些地方是考点!!!
题 目 解 析
我们还以 TPO17 L4 为例,来看一下 lecture 的论点和分论点是如何对应考题的。
(1) What is the lecture mainly about ?
A. Different kinds of color vision in sea animals.
B. Differences in appearance between various species of octopus.
C. Ways that octopuses attract their prey.
D. Ways that octopuses protect themselves from predators.
(2) Why does the professor first mention Proteus?
A. To explain how the octopus got its scientific name.
B. To introduce the octopus’ exceptional abilities.
C. To point out that the octopus played an important role in Greek mythology.
D. To provide an example of a mythological character that was part animal and part human.
第三题：考察how to change color，对应分论点二。
(3) How does an octopus change color to match the colors in its environment? Click on 2 answers
A. By raising its papillae.
B. By releasing colored ink.
C. By reflecting light from its environment.
D. By contracting the muscles around its chromatophores.
第四题：考察how to change texture部分，对应分论点三。
(4) What does the professor say about the function of the papillae?
A. They produce dye in different colors.
B. They propel the octopus through the water.
C. They change the texture of the octopus’ skin.
D. They help the octopus contract into a smaller shape.
第五题：考察how to change size and shape 部分，对应分论点四。
(5) What two examples does the professor mention to describe the octopus’ ability to change its shape? Click on 2 answers
A. A small round stone
B. The leaves of a plant
C. A cloud of ink.
D. A piece of coral.
第六题：重听题。重听部分听到的是例子细节。老师上课为什么会举例子呢?举例子的目的当然是帮助同学们理解某个知识点，所以该题的答案是 illustrate a point 阐明观点。
(6) Why does the professor say this
A. To point out an error.
B. To illustrate a point.
C. To propose an explanation.
D. To correct a misunderstanding.
总结一下，托福听力 lecture 结构的大原则就是：总分总!!在这个大原则的基础上，每篇 lecture 具有自己的小特点，例如有的教授喜欢举例子，有的教授喜欢讲理论，还有的教授喜欢做实验，lecture 结构不同考点出现的位置也就不一样。