托福聽力lecture并列型分析

　　之前我們介紹了lecture的并列型結構，一般是圍繞某一個主題并列平行展開去講解。這類結構沒有之前我們見到的直線型結構那么好區(qū)分，因為他沒有明顯的表示時間地點人物的信號詞，但是這種結構類型是我們TPO和考試中出現(xiàn)的比較多的結構類型。我們這次分析一篇按并列結構分層的一篇文章
　　今天我們以TPO13-L4為例，給大家講解一下。
　　OK, I wanna go over the different types of meteorites, and what we've learned from them about the formation of Earth, and the solar system. Uh… the thing is what's especially interesting about meteorites is that they come from interplanetary space, but they consist of the same chemical elements that are in matter originating on Earth, just in different proportions. But that makes it easier to identify something as a meteorite, as opposed to…to  just a terrestrial rock.
　　要注意文章一開始的地方就說出了今天的主題——meteorite。并且后面也一直在重復這個詞。
　　So to talk about where meteorites come from, we need to talk about comets and asteroids, which basically...they’re basically made up of debris left over from the origin of the solar system 4.6 billion years ago.之后提出屏幕提示的信息comets and asteroids，幫助我們理解meteorite
　　Now I'm going a bit out of a order here…um…I'm not going to go into any depth on comets and asteroids now, but we'll come back later and do that. For now, I'll just cover some basic info about them.并且同是講到兩種不同的行星來進行對比，讓我們清楚的理解這幾個詞之間的關系
　　Relatively near the sun, in the inner solar system, between Jupiter and Mars to be precise, we’ve got the asteroid belt, which contains about 90 percents of all asteroids orbiting the sun. These asteroids are…uh…like the terrestrial planets, in that they're composed mostly of rocky material and metals.
　　Far from the sun, in the outer solar system, beyond Jupiter's orbit, temperatures are low enough to permit ices to form out of water and…and out of gases like methane and carbon dioxide. Loose collections of these ices and small rocky particles form into comets. So comets are similar in composition to the gas giants.
　　Both comets and asteroids are...typically are smaller than planets. An even smaller type of interplanetary debris is the meteoroid. And it's from meteoroids that we get meteors and meteorites. "Roids" are, for the most part anyway, they are just smaller bits of asteroids and comets. When these bits enter Earth’s atmosphere, well, that makes them so special that they get a special name. They're called meteors. Most of them are very small, and they burn up soon after entering Earth’s atmosphere. The larger ones that make it through the atmosphere and hit the ground are called meteorites. So meteorites are the ones that actually make it through.之后緊接著講到另一個屏幕提示詞meteoroid，并且直接講到這幾個詞直接的關系。之后回到一開始的主題詞meteorite，并且開始具體將其分為三類：stones, stony irons and irons.
　　Now we've been finding meteorites on Earth for thousands of years, and we've analyzed enough of them to learn a lot about their composition, most come from asteroids, though a few may have come from comets. So essentially they are rocks, and like rocks, they're mixtures of minerals. They are generally classified into three broad categories--stones, stony irons and irons.
　　Stone meteorites, which we refer to simply as, uh, stones, are almost entirely rock material. They actually account for almost all of the meteorite material that falls to earth. But even so, it's rare to ever find one. I mean, it's easier to find an iron meteorite or a stony iron. Anyone guess why? Look at their names. What do you think iron meteorites consist of?文章最后的重點放在餓了Stone meteorites，并且就這個信息描述了兩點：首先它是最多的隕石類型，其次，雖然數(shù)量很多但是我們確很難找到這種隕石，因為它的成分基本是石頭
　　Mostly iron?
　　Yeah… iron and some nickel, both of which are metals. And, if you're trying to find metal?
　　Oh! Metal detectors!
　　Right, thank you. At least that's part of it. Stone meteorites, if they lie around exposed to the weather for a few years, well, they're made of rock, so they end up looking almost indistinguishable from common terrestrial rocks--ones that originated on earth. So it's hard to spot them by eye. But we can use metal detectors to help us find the others, and they're easier to spot by eye. So most of the meteorites in collections, uh, in museums, they'll be...they're iron meteorites, or the stony iron kind, even though they only make up about 5 percent of the meteorite material on the ground.