【正文】 s came to North America. Student: Yeah, well, there used to be beavers all over the place, something like 200 million beavers, just in the continental United States. But when Europeans came, they started hunting the beavers for their fur, because beaver fur is really warm, and it was really popular for making hats in Europe. So the beavers were hunted a lot, overhunted, they are almost extinct by the 1800s, so… that meant fewer wetlands, less standing water. Professor: And what does that mean for the ecosystem? Kate? Student: Well if there is less standing water than the ecosystem can support its many species, because a lot of insects and fish and frogs can39。 you might read up on cushy stage of cognitive development we covered those in class. Student: Aha… Professor: And most likely, what stage would a child of that age be in? Student: Um… the pre operational stage? Professor: Exactly, if that’s the case, her languages used to be maturing and her memory and imagination would be developed. Student: So she might play pretend like she can pretend when driving her toy car across a couch that the couch is actually a bridge or something. Professor: That is right. In addition, her thinking would be primarily egocentric. Student: So she would be thinking mostly about herself and her own needs, and might not be able to see things from anyone else perspective. Professor: En hums… Student: But what if she doesn’t? I mean, what if she doesn’t demonstrate those behaviors? Professor: That’s fine。s something about wetland, and ground water too. Professor: OK, good. Wetlands have a big affect on ground water, the amount of water below the surface of the land. Think of wetlands as, Umm, like a giant sponge, the earth soaks up a lot of this water that39。t want to miss anything, you know, and it is probably already started watching it... Manager: No problem, we39。ve analyzed enough of them to learn a lot about their position, most e from asteroids, though a few may have e from ets. So essentially they are rocks, and like rocks, they39。re made of rock, so they end up looking almost indistinguishable from mon terrestrial rocksonce that originated on earth. So it39。s especially interesting about meteoroids is that they e from interplaary space, but they consist of the same chemical elements that are in matter originated on earth, just in different proportions. But that makes it easier to identify something as a meteoroid, as it opposed to…to just a terrestrial rock. So to talk about where meteoroids e from, we need to talk about ets and asteroids, which basically...they’re basically made up of debris left over from the origin of the solar system billion years ago. Now I39。s the critical species that keeps the system going. Now, beaver populations are on the rise again, but there is something to think about. Consider humans as part of these ecosystems, you39。s we39。s so important, cause if you go back before European settled in north America, like before the 1600s, back when native Americans were the only people living here, well, back then there were a lot of beavers, but later on, after Europeans… Professor: OK, wait, I see where you are heading with this, but before we go into how European settlement affected the ecosystem, tell me this what kind of environment do beavers live in? Think about what it was like before the Europeans settlers came, we’ll e back to where you were headed. Student: OK, well, beavers live near streams and rivers and they block up the streams and rivers with like logs and sticks and mud. You know, they build dams that really slow down the flow of the stream. So then the water backs up, and creates like a pond that floods the nearby land. Professor: And that creates wetlands. OK, tell me more. Student: Well with wetlands, it39。t take any videos out of the lab. Student: OK, so how long can I use the video room for? Manager: You can sign up for two hours at a time. Student: Oh, good, so I can watch more than one video when I e up here. Is the lab pretty busy all the time? Manager: Well, rooms are usually full read after dinner time, but you can sign up the day before to reserve the room if you are. Student: Err...the day before....But, I can just stop in to see if the any lab is open, right? Manager: Sure, stop in any time. Student: What about copies of these videos? Is there just one copy of each in the series? I don39。s from meteoroids that we get meteors and meteorites. Roids are, for the most part anyway, they are just smaller bits of asteroids and ets. When these bits enter earth’s atmosphere, well, that makes them so special that they get a special name. They39。ll be...they39。ll e back later and do that. From now, I39。m not sure, but err... is this the Carter language lab? Manager: Yes, it is. How can I help you? Student: I39。s locat