托福听力每日一练第40天：
演讲听写训练1：
I’m going to pass this piece of amber around so you can see this spider trapped inside it. It’s a good example of amber-inclusion, one of the inclusions that scientists are interested in these days. This particular piece is estimated to be about 20 million years old. Please be extremely careful not to drop it. Amber shatters as easily as glass. One thing I really like about amber is its beautiful golden color.
Now, how does the spider get in there? Amber is really fossilized tree resin. Lots of chunks of amber contain insects like this one or animal parts like feathers or even plants. Here is how it happens. The resin oozes out of the tree and the spider or leaf gets incased in it. Over millions and millions of years, the resin hardens and fossilizes into the semiprecious stone you see here.
Ambers can be found in many different places around the world. But the oldest deposits are right here in the United States, in Appalachian. It’s found in several other countries, too, though right now scientists are most interested in amber coming from the Domincian Republic. Because it has a great any inclusions, something like one insect inclusion for every one hundred pieces. One possible explanation for this it that the climate is tropical and a greater variety of number of insects thrive in tropics than in other places. What’s really interesting is the scientists are now able to recover DNA from these fossils and study the genetic material for important clues to revolution.
演讲听写训练2：
Now we’ve been talking about the revolutionary period in the United States history when the colonies wanted to separate from England. I’d like to mention one point about the very famous episode from that period, a point I think is pretty relevant even today. I’m sure you remember, from when you are children, the story of Paul Revere’s famous horseback ride to the Massachusetts countryside. In that version, he single-headily alerted the people that “the British were coming”. We have this image of us solitary rider galloping along in the dark from one farm house to another. And of course the story emphasized the courage of one man, made him a hero in our history books, right? But, that rather romantic version of the story is not what actually happened that night. In fact, that version misses the most important point entirely. Paul Revere was only one of the many riders helping deliver the message that night. Just one part of a pre-arrange plan, that was thought out well in advance in preparation for just such an emergency. I don’t mean to diminish Revere’s role though. He was actually an important organizer and promoter of this group effort for freedom. His mid-night riders didn’t just go knocking on farm house doors. They also awaken the institutions of New England. They went from town to town and engage the town leaders, the military commanders and volunteer groups, even church leaders, people who would then continue to spread the word. My point is that Paul Revere and his political party understood, probably more clearly than later generations ever have, that political institutions are there as a kind of medium for the will of people and also to both build on and support individual action. They knew the success requires careful planning and organization. The way they went about the work that night made a big difference in the history of this country.
演讲听写训练3：
Let me warn you against a mistake that historians of science often make. They sometimes assume that people in the past use the same concepts as we do. There is a wonderful example that made news in the history of mathematics some while ago. It concerns an ancient Mesopotamian tablet that has some calculations on it using square numbers. The calculations look an awful lot like the calculations of the length of the sides of triangle. So that’s what many historians assume they were. But using square numbers to do this is a very sophisticated technique. If the Mesopotamians knew how to do it, as the historians started thinking that they did. Well, then their math was incredibly advanced. Well, it turns out the idea of Mesopotamians use square numbers to calculate the length of triangle’s sides is probably wrong. Why? Because we discovered that Mesopotamians didn’t know how to measure angles, which is a crucial element in the whole process of triangle calculations. Apparently the Mesopotamians had a number of other uses for square numbers. These other uses were important but they were not used with triangles. And so these tablets in all likelihood were practice sheets, if you like, for doing simpler math exercises with square numbers. In all likelihood, it was the ancient Greeks who first calculate the length of triangle’s sides using square numbers. And this was hundreds of years after the Mesopotamians.
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