托福听力讲座4条解题原则分享 应对难题更轻松
1、主旨题找线索遵循首尾原则
众所周知，绝大多数讲座的行文方式都是由教授开门见山地讲述通篇的主旨，所以针对主旨题必须听明白的就是首段了。结尾方式则比较多样化，时而首尾呼应，时而深化主题，甚至有的时候会出现一些和开始不一致或者相反的结论，这时主旨题的正确选项则应该从结尾处对应获得。
2、文章结构题按照顺序原则记重点
一般来讲，如果听到类似基数词“one, two, three”，或者序数词“first, second, third”，亦或像逻辑顺序词“to start off, to begin with, and, another, also, something else”。还有“yet another, last but not least, that’s when the concept of X comes into the picture”之类的信息，那么这篇讲座的结构一般就可以被轻松地定性为是“总分结构”，而且考生应该了解，所有上述的提示词之后必定会出现一个分论点，必须做记录，因为对应会考查细节题。
3、推断题必须把握好定义原则
一旦文章当中出现了针对某个词或者某个概念的定义性解释，那么这个被解释的词或者概念一定我们笔记的重中之重。因为这个词对于大多数考生来说往往是一个完全陌生的概念，而且对这个词的理解程度很可能会直接影响我们对整篇文章的理解程度，因为文章的其它部分或许就是因为这个概念而展开的。很多推断题就是基于某个定义而考查的。
4、细节题请重视举例原则
平时生活中我们举例子的目的就是为了用一个具体的实例去解释抽象的概念，在托福听力中也不例外。那么大家除了要听到“for instance, let’s take X as an example”这类短语，还要留意诸如“say, it can, one typical” 这类词，而且一定要知道这些实际的例子到底是为了解释哪个抽象的概念才存在的，也就是说，一定要找出分论点和细节之间的对应关系，切勿犯了张冠李戴的错误。题目方面可以设置成：在题干中给出分论点，要求选出对应细节的细节题;也可以设置成，在题干中给出细节，要求选出对应分论点的组织结构题。
2020托福听力练习：聚焦节能的白光发明
LEDs use only a quarter the energy of incandescent bulbs. But despite their efficiency, there is one thing they're not that good at: "They have a hard time giving directional light." Sangam Chatterjee, a physicist at the University of Marburg and the University of Giessen, in Germany.
Chatterjee and his colleagues may have fixed that. They devised a highly focused, but still energy-efficient light beam, by starting with something that's already a highly focused beam: a laser. The key is what they shoot the laser at: a substance with a particular structure. "I'm always tempted to say "white powdery substance" but I guess there's some connotation on that."
They synthesized the material from cages of tin and sulfur atoms decorated with hydrocarbon molecules. The laser-produced infrared light — which the human eye cannot see — goes in, but what comes out are many different optical wavelengths. "It's a molecular light converter. It basically changes the color of the light, while retaining the directionality of the lasers. So you can make something like a white laser beam containing many, many colors." That mix of colors, overall, glows bright white, like a halogen bulb in a beam. The study is in the journal Science.
This sort of low-energy focused white beam could be used for the very small — like a light source for microscopes — to the very big. "You could use this for a spotlight in the theater. And in the end it should be much more energy efficient than the typical standard spotlight." Meaning focused white light…that takes a little heat off the environment.
LED灯使用的电量仅为白炽灯的1/4。虽然LED灯高效节能，但是它们也有不擅长的事情：“它们不能发射平行光。”桑伽姆·查特吉是德国马尔堡大学和吉森大学的物理学家。
查特吉和他的同事可能已经解决了这个问题。他们通过高度聚焦的光束——激光，发明了一种高度聚焦且节能的光束。关键就是用激光照射一种拥有特殊结构的物质。“我一直想说是白色粉状物质，不过我想关键是内部的东西。”
他们用烃分子修饰的锡和硫原子合成了这一材料。激光发出的红外线肉眼看不到，红外线进入后会产生很多不同的波长。“这是一种分子光转化器。可以改变光的颜色，但同时保留激光的方向性。这样就可以制造出含有很多种颜色的白色激光束。”混合的颜色就会发出像卤素灯泡一样的亮白色光束。这一研究结果发表在《科学》杂志上。
这种低能聚焦白色光束既可以应用于显微镜光源这种小物件上，也可以应用到大场合。“这种光束可以用作剧院的聚光灯。比普通的标准聚光灯更加节能。”这表明聚焦白光可以消耗环境中的一部分热量。
谢谢大家收听科学美国人——60秒科学。我是克里斯托弗·因塔利亚塔。
重点讲解：
1. be good at 擅长的;精通的;能干的;
例句：He is good at mental arithmetic.
他擅长心算。
2. start with (以做某事) 开始;
例句：I wanna start with a song that means a lot to me.
我打算由一首对我意义非凡的歌开始。
3. be tempted to do sth. 想做…的;希望做的;
例句：I was sorely tempted to complain, but I didn't.
我极想发牢骚，但还是没开口。
4. in the end 最终;
例句：He debated buying a new car, but didn't in the end.
他思量很久是否买辆新汽车，但最后还是没买。
2020托福听力练习：桦树在夜晚进入睡眠
This is Scientific American — 60-Second Science. I'm Cynthia Graber.
Many people remember the colors of the rainbow by the acronym ROY G. BIV. For red, orange, yellow, green, blue, indigo and violet. Well, the color indigo just made news.
Indigo gets its name from the plant Indigofera tinctoria and its relatives, which supply the dye that makes fabric the rich, beautiful color between blue and violet.
Indigo dye was used around the ancient world in fabrics created from Egypt to China to Meso and South America. And it's in South America that researchers recently found the oldest known example of fabrics dyed with indigo.
The artifacts were discovered at Huaca Prieta, a ceremonial mound on the coast in northern Peru. But their color was initially hidden by the grey tones that had leached into them from the materials used in the mound itself. But when a conservator carefully washed the fabric, the true colors reappeared.
"And it was at that point that I realized we probably had indigo and it was probably the world's oldest indigo."
Jeffrey Splitstoser, an anthropologist at George Washington University.
"Which was really exciting. I hadn't thought I'd be discovering, or we would be discovering, the world's oldest indigo, when I took on this project."
The research is in the journal Science Advances.
The dyed fabric is about 6,000 years old.
"In the Middle East there are inscriptions that discuss blue fabrics that date to about 3100 B.C. These are just texts though. And so we think they're referring probably to the earliest Old World indigo-blue dyed textiles. So that would date to about 5,000 years ago, 3100 B.C. And so these are at least 1,000 years older than that. And the earliest known indigo blue textiles were from Egypt and they date to around 4400 B.P., before present. So these are almost 2,000 years older than those."
Splitstoser says that the discovery means it's likely that the techniques to dye fabric blue were developed in the Americas before they were developed in Egypt.
"It really means that we have to look at the ancient Andes as one of the earliest sources of textile innovations in the world."
许多人记得彩虹的颜色按照首字母排列为ROYGBIV。这些首字母分别代表红、橙、黄、绿、蓝、靛、紫。而靛色最近有了新的消息。
靛蓝色得名于木蓝以及其相关植物，这些植物可以提供染料，让布料变成介于蓝色和紫色之间的一种富贵、美丽的颜色。
靛蓝染料在古代用于对布料进行染色，而这些布料一般产自埃及、中国、中美洲以及南美洲等地方。最近，研究人员就在南美洲发现了目前已知最古老的靛蓝染色布料。
人们在普雷塔遗址发现了这些手工艺品，普雷塔遗址位于秘鲁北部海岸，是一个曾用于举行仪式的土丘。但是这些手工艺品的颜色最初被灰色基调所掩盖，而灰色来自于土堆本身材料的渗透。但是，当一位文物修复员仔细清理这些布料后，其真正的颜色重新显现出来。
“就在那时我意识到，我们发现的可能是是靛蓝色，而且这可能是世界上最古老的靛蓝色。”
杰弗里·斯皮里特瑟是乔治华盛顿大学的人类学家。
“这太让人兴奋了。我在做这个项目的时候，从来没想过我或者说我们会发现世界上最古老的靛蓝色。”
这项研究发表在《科学进展》期刊上。
这块染色布料大约有6000年的历史。
约公元前3100年，在中东有讨论蓝色布料的铭文。虽然这些只是文字材料。不过，我们认为它们指的可能是最古老的靛蓝色纺织品。因此，靛蓝色染料的历史可追溯到5000年前，即大约公元前3100年。而这些新发现的染色布料至少要早1000年。此前已知最古老的靛蓝色纺织品来自于古埃及，距今大约4400年。所以，新发现的染色布料比那些要早约2000年。
斯皮里特瑟表示，这一发现表明，美洲发明将布料染成蓝色的技术很可能早于埃及。
“这实际上意味着，我们必须将古安第斯地区视为世界上织物创新最早的起源地之一。”
重点讲解：
1. take on 承担，接受(尤指艰巨工作或重大责任);
例句：He is ready to take on heavy responsibilities.
他乐于承担重担。
2. refer to 提到，指的是;
例句：It can refer to an academic subject or a practical skill.
这一词既可指某一学科也可指某种技能。
3. at least (数量)至少，不少于;
例句：Cacao has been cultivated for at least three millennia in Mexico, Central and South America.
在墨西哥及中南美洲，可可树至少已有了三百万年的种植历史。
