原创TPO8托福阅读Passage1原文文本+题目+答案解析

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官方真题Official8托福阅读Passage1原文文本

The Rise of Teotihuacán

The city of Teotihuacán, which lay about 50 kilometers northeast of modern-day Mexico City, began its growth by 200-100 B.C. At its height, between about A.D. 150 and 700, it probably had a population of more than 125,000 people and covered at least 20 square kilometers. It had over 2,000 apartment complexes, a great market, a large number of industrial workshops, an administrative center, a number of massive religious edifices, and a regular grid pattern of streets and buildings. Clearly, much planning and central control were involved in the expansion and ordering of this great metropolis. Moreover, the city had economic and perhaps religious contacts with most parts of Mesoamerica (modern Central America and Mexico).

How did this tremendous development take place, and why did it happen in the Teotihuacán Valley? Among the main factors are Teotihuacán’s geographic location on a natural trade route to the south and east of the Valley of Mexico, the obsidian resources in the Teotihuacán Valley itself, and the valley’s potential for extensive irrigation. The exact role of other factors is much more difficult to pinpoint―for instance, Teotihuacán’s religious significance as a shrine, the historical situation in and around the Valley of Mexico toward the end of the first millennium B.C., the ingenuity and foresightedness of Teotihuacán’s elite, and, finally, the impact of natural disasters, such as the volcanic eruptions of the late first millennium B.C.

This last factor is at least circumstantially implicated in Teotihuacán’s rise. Prior to 200 B.C., a number of relatively small centers coexisted in and near the Valley of Mexico. Around this time, the largest of these centers, Cuicuilco, was seriously affected by a volcanic eruption, with much of its agricultural land covered by lava. With Cuicuilco eliminated as a potential rival, any one of a number of relatively modest towns might have emerged as a leading economic and political power in Central Mexico. The archaeological evidence clearly indicates, though, that Teotihuacán was the center that did arise as the predominant force in the area by the first century A.D.

It seems likely that Teotihuacán’s natural resources, along with the city elite’s ability to recognize their potential, gave the city a competitive edge over its neighbors. The valley, like many other places in Mexican and Guatemalan highlands, was rich in obsidian. The hard volcanic stone was a resource that had been in great demand for many years, at least since the rise of the Olmecs (a people who flourished between 1200 and 400 B.C.), and it apparently had a secure market. Moreover, recent research on obsidian tools found at Olmec sites has shown that some of the obsidian obtained by the Olmecs originated near Teotihuacán. Teotihuacán obsidian must have been recognized as a valuable commodity for many centuries before the great city arose.

Long-distance trade in obsidian probably gave the elite residents of Teotihuacán access to a wide variety of exotic good, as well as a relatively prosperous life. Such success may have attracted immigrants to Teotihuacán. In addition, Teotihuacán’s elite may have consciously attempted to attract new inhabitants. It is also probable that as early as 200 B.C.Teotihuacán may have achieved some religious significance and its shrine (or shrines) may have served as an additional population magnet. Finally, the growing population was probably fed by increasing the number and size of irrigated fields.

The picture of Teotihuacán that emerges is a classic picture of positive feedback among obsidianmining and working, trade, population growth, irrigation, and religious tourism. The thriving obsidian operation, for example, would necessitate more miners, additional manufacturers of obsidian tools, and additional traders to carry the goods to new markets. All this led to increased wealth, which in turn would attract more immigrants to Teotihuacán. The growing power of the elite, who controlled the economy, would give them the means to physically coerce people to move to Teotihuacán and serve as additions to the labor force. More irrigation works would have to be built to feed the growing population, and this resulted in more power and wealth for the elite.

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现在大家在进行托福备考时官方真题Official托福模考软件相信是大家用的最多的工具了，对于托福成绩的提升是非常有帮助的。托福听力可以说是整个托福考试当中比较重要的一个部分，如何利用现有资料官方真题Official模考软件来提升大家的托福成绩呢?今天小编在这里整理了官方真题Official8托福听力Lecture4文本+题目+答案解析来分享给大家，希望对大家托福听力备考有帮助。

官方真题Official8托福听力Lecture4原文文本

Narrator: Listen to part of a lecture in a Chemistry class. The professor has been discussing the periodical table of elements.

Pro: So, are there any questions?

Stu: Yes, um, Professor Harrison, you were saying that the periodic table is predictive. What exactly does that mean? I mean I understand how it organizes the elements, but where’s the prediction?

Pro: Ok, let’s look at our periodic table again. Ok, it groups elements into categories that share certain properties, right?

Stu: Uh-huh.

Pro: And it is arranged according to increasing atomic number, which is…

Stu: The number of protons in each atom of an element.

Pro: Right. Well, early versions of the periodic table had gaps, missing elements. Every time you had one more proton, you had another element. And then, oops, there’d be an atomic number, for which there was no known element. And the prediction was that an element with that atomic number existed somewhere, but it just hadn’t been found yet. And its location in the table would tell you what properties it should have. It was really pretty exciting for scientists at that time to find these missing elements and confirm their predictive properties.

Um, actually, that reminds me of a ... of a very good example of all these, element 43. See on the table, the symbols for elements 42 and 44. Well, in early versions of the table, there was no symbol for an element 43 protons because no element with 43 protons had been discovered yet. So the periodic table had a gap between elements 42 and 44.

And then in 1925, a team of chemists led by a scientist named Ida Tacke claimed that they had found element 43. They had been using a relatively new technology called X-ray spectroscopy, and they were using this to examine an ore sample. And they claimed that they’d found an element with 43 protons. And they named it Masurium.

Stu: Um, Professor Harrison, then, how come in my periodic table here, element 43 is Tc? That’s Technetium, right?

Pro: Ok, let me add that. Actually, um, that’s the point I’m coming to. Hardly anyone believed that Tacke’d discovered a new element. X-ray spectroscopy was a new method at that time. And they were never able to isolate enough Masurium to have a weighable sample to convince everyone of the discovery. So they were discredited. But then, 12 years later in 1937, a different team became the first to synthesize an element using a cyclotron. And that element had…

Stu: 43 protons?

Pro: That’s right, but they named it Technetium to emphasize that it was artificially created with technology. And people thought that synthesizing this element, making it artificially was the only way to get it. We still hadn’t found it occurring in nature. Now element 43, whether you call it Masurium or Technetium, is radioactive. Why does that matter? What is true of a radioactive element?

Stu: It decays, it turns into other elements. Oh, so does that explain why it was missing in the periodic table?

Pro: Exactly, because of its radioactive decay, element 43 doesn’t last very long. And therefore, if that ever had been present on Earth, it would have decayed ages ago. So the Masurium people were obviously wrong, and the Technetium people were right. Right? Well, that was then.

Now we know that element 43 does occur naturally.It can be naturally generated from Uranium atoms that have spontaneously split. And guess what, the ore sample the Masurium group was working with had plenty of Uranium in it, enough to split into measurable amounts of Masurium. So Tacke’s team might very well have found small amounts of Masurium in the ore samples. It’s just that once was generated from split Uranium, it decayed very quickly.

And you know here’s an incredible irony. Ida Tacke, the chemist led the Masurium team, well, she was the first to suggest that Uranium could break up into smaller pieces, but she didn’t know that that was the defense of her own discovery of element 43.

Stu: So is my version of the periodic table wrong? Should element 43 really be called Masurium?

Pro: Maybe, but you know it’s hard to tell for sure after all this time, if Ida Tacke’s group did discover element 43. They didn’t, um, publish enough detail on their methods or instruments for us to know for sure.

But I’d like to think element 43 was discovered twice. As Masurium, it was the first element discovered that occurs in nature only from spontaneous fission, and as Technetium, it was the first element discovered in a laboratory. And of course, it was an element the periodic table let us to expect existed before anyone had found it or made it.

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