欢迎来的Day5-Part2的学习，在这里我们会练习两篇文章。一篇Archaeology和一篇Environmental Science。

Day5-Lecture2

Step1：听文章音频，计时3分30秒做题。（20分以下的同学，建议不做或者尽量少做笔记）

题目：

1. What is the main purpose of the lecture?

A To describe how archaeologists create maps of sites they have excavated

B. To describe an important event in Mayan history

C. To describe how a specific technology has changed archaeological research

D. To illustrate how an ancient civilization developed agricultural techniques

2. Why does the professor mention explorers cutting a path through the rain forest?

A. To recount a memory of her experiences as an archaeologist

B. To express a concern about damage to rain forests

C. To show why some archaeologists prefer not to work in rain forests

D. To correct a misunderstanding about the practice of archaeology

3. What is one benefit of lidar mentioned by the professor?

A. It works in all types of weather conditions 

B. It detects structures that are buried under plant growth.

C. It does not require the use of a Global Positioning System. 

D. It provides information about the plant species at a site. 

4. What can be inferred from the results of lidar mapping at Caracol?

A. The Maya were skilled at designing complex cities. 

B. Caracol was much older than archaeologists realized. 

C. Caracol was the first site in Belize to use terraced fields. 

D. The Maya civilization began to decline in 650 C.E. 

5. How did the inhabitants of Caracol grow enough food to sustain a large population?

[Click on 2 answers]

A. By having each town specialize in a particular crop 

B. By collecting rainwater for watering the fields

C. By planting crops that grow rapidly 

D. By using all available space for planting crops

6. What is the professor's opinion about the cost of lidar mapping? 

A. The cost will decrease as lidar mapping becomes more common. 

B. The cost of lidar mapping is not as high as some people claim. 

C. Lidar mapping is worth the cost because identifying good sites to investigate saves money

D. Researchers will need new sources of funding before they can afford lidar mapping.

Listen to part of a lecture in an archaeology class. 

It's a popular image of archaeology, the machete-wheeling explorers cutting and chopping their way through a wilderness in search of lost civilizations. Well, they often do need machetes when they're traversing a rainforest, but it's not as glamorous as it looks in the movies and not as easy. Finding and mapping ancient sites is slow, tedious(冗长的), sweaty work. (2)

[Couldn't they just fly over the rainforest in an airplane and take photographs?] 

There are certainly advantages to viewing a site from above. However, if the site is thickly covered with vegetation, aerial photography doesn't provide enough detail, because the view is blocked by the trees. It wouldn't be much use in areas covered by rainforest. Fortunately, we do have mapping technology that can reveal structures hidden below the vegetation. It's called Lidar, which stands for light detection and ranging. (1) (3)

Here a lidar works, a pilot flies a small plane back and forth over a site in a grid pattern. While flying, the plane beams a stream of laser signals at the ground below. The signals bounce back(反弹). The amount of time it takes for each signal to bounce back is automatically recorded. What does that tell us? Well, variations(差异) in these bounce back times indicate variations in the elevation of the surface below. 

The plane also contains a GPS device. GPS device links with a global positioning system, that's a network of space satellites that uses radio waves to identify locations on earth. The plane’s GPS device uses information from the satellites to record the position and orientation(方向) of each lidar signal that bounces back. The results are analyzed by a computer, and what you end up with is a map that shows all the structures on the surface, even if they're concealed under abundant plant growth. It looks very much like a three dimensional(3D) map. 

[Are you saying that lidar can see right through leaves? ]

The signals don't actually penetrate through foliage, but there are enough tiny gaps between these where the signals get through. But let's see a site has a smooth covering with no gaps at all, like a layer of volcanic ash, for instance. Lidars are no use at a site like that, nor does it work at sites where the weather is always wet. Laser signals don't travel through rain, snow or fog. 

Plus, it's got to be expensive. The plane and the equipment and everything. 

Well, that's true, of course, but in terms of what it delivers, lidar can change our understanding of a whole civilization almost overnight. (6) Here's an example. There's a site in Belize called Caracol. It was built centuries ago by the Mayas civilization. Over the course of time, Caracol was completely overgrown(覆盖) by rainforest. A group of archeologists began exploring it in the 1980s using the old fashioned methods, walking through the forest. It appeared to be a small place that was occasionally used for public ceremonies. Then in 2009, these archaeologists decided to give Lidar a try. At the end of the mere three weeks, BAM! They had all the evidence they needed to show that Caracol, in the year 650 C.E, was a metropolis with the population of more than 100,000. (4)

[100,000 people! Is that even possible for that era? How did everyone have enough to eat? ]

Because Caracol wasn't just a city, it was a brilliantly design, comprehensive land use system. The inhabitants(居民) lived in well spaced towns that were connected to the city center by a network of roadways. Every bit of land that could be used for growing food was put to use. (5-D) Between the towns were fields. They were laid out as terraces running horizontally across entire hillsides, an excellent way to retain water and stop erosion. And because the Maya collected water during the rainy season, especially built reservoirs(水库), They were able to grow food year round and get multiple harvests out of the fields. (5-B)

And the archaeologists had missed all of that, even the terraces(梯田)? 

Yes, because the ruins of these structures are completely covered by vegetation. They all look like part of the terrain. 

[So are they going to go back and do light or mapping of all the ancient sites? ]

Yes, if it's feasible, because without it, we're trying to draw conclusions from inadequate information. As for the cost, once lidars are done, it shows archaeologists exactly where to dig, so they don't waste their time or their money poking around the wrong places. (6)

答案：

C D B A BD C

Step2：观看错题或不确定的题目对应的讲解视频。（18分以下的同学建议每题都看一下，这样更扎实一些。）

第一题

第二题

第三题

第四题

第五题

第六题

看完讲解大家应该对题目应该没有疑问了，如果是思路问题和选项理解问题导致的错题需要进行总结，建议把题目截图放到word/pages或者其他文档中，然后简单描述一下自己错题的思路。每周都建议一下错题，尽量避免重复犯错。（18分以下的同学可以暂时忽略这个步骤，主要问题应该还是在文章理解上。）

接下来又是最为艰苦卓绝的听译环节，这步坚持下来练习就等于完成了一大半。