托福tpo9套听力真题文本

托福tpo9套听力真题文本内容摘要：

erature increase has occurred during the winter and spring, not during the summer. Butthe increase in shrubs has occurred in the how can increase temperaturesin thewinter and spring result in increased shrub growth in thesummer? Well, it may be biological processesthat occur in the soil in thewinter,that cause increased shrub growth in thesummer,and here39。 show: thereare microbes, microscopic anisms that live in the soil. These microbes enable the soil to have more nitrogen, which plants needto live and theyremain quite active during the 39。 retwo reasons for this: first, theylive in the active layer,which, remember,containswater that doesn39。 t peratethe permafrost. Second, most of the precipitation in the 全国免费咨询电话： 4000123267 Arctic is in the form of the snow, which blankets theground in the winter,actually has an insulating effect on the soil beneath it. And it allows the temperature ofthe soil to remain warm enough for microbesto remain active. So there39。 sbeen increase in nutrient production in the that39。 swhat39。 s responsible for thegrowth ofshrubs in the summer and their spread tonew areasof the tundra. Areaswith more new nutrients arethe areas with the largest increase in shrubs. Female student: But,what about runoff in the spring, when thesnow finally melts? Won39。 t the nutrientsgetwashed away? Spring thaw always washes away soil, doesn39。 t it? Lecturer:Well, much ofthe soil is usually still frozen during peak runoff. And the nutrientsare deep down in the active layer anyway, not high up near the surface, which is the part of theactive layer most affected byrunoff. Butas I was about to say, there39。 smore to tundra is windy,and the snow is blown across thetundra, it39。 s caught by shrubs. And deep snow drifts often form around shrubs. And we39。 ve alreadymentioned theinsulating effect of snow. So that extra warmth means evenmore microbial activity, which means even more food for the shrubs, which means even more shrubs and more snow around etc..It39。 sa circle, a loop. And because of this loop, which is promoted by warmertemperaturesin winterand spring, well, it looks like the tundra may be turning into shrub land. 全国免费咨询电话： 4000123267 Female student: But willit be long term?I mean maybe the shrubs will be abundant for a few years, and then it39。 ll change back to tundra. Lecturer:Well, shrub expansion has occurred in otherenvironments, like semiarid grassland, and tall grass prairies. And shrub expansion in these environmentsdoes seem to persist, almost to thepoint of causing a shift. Once is established, shrub land thrives, particularly in theArctic, because Arctic shrubs are good at taking advantage ofincreased nutrientsin the soil, better than other Arctic plants. SECTION 2 TPO9_Listening_2_1 Listen to a conversation between a student and a librarian employee. S: Excuse me. Can you help me with something? L: I39。 lldo do you need? S: Well, I39。 ve received a letter in mymailbox saying that I39。 m supposed to return a book that I checked out back in January,it39。 s callModern Social Problems. But because I39。 m writing my senior thesis, I39。 msupposed to be able tokeep the book all semester. L: So you signed up for extended borrowing privileges? S: Yeah. L: Butwe are still asking you tobring the book back? S: Enhen. 全国免费咨询电话： 4000123267 L: Well,let me takea look and see what the putersays. The title was Modern Social Problems? S: Yeah. L: OK. Oh, I see,it39。 s been recalled. You can keepit all semester as long as no one else requestsit. But,someone else has. It looks like one of the professors in the sociology departmentrequested you have to bring it back, even though you39。 ve got extended borrowing privileges. You can checkout thebook again when it39。 s returned in a couple ofweeks. S: But I reallyneed this book right now. L: Do you needall of it or is therea certain section or chapteryou39。 re working with? S: I guess thereis one particular chapterI39。 ve been using lately for a section of mythesis. Why? L: Well,you can photocopyup to one chapterof the book. Why don39。 t you do that for the chapteryou39。 re working on right now? And by the timeyou need the rest ofthe book, maybe it will have been returned. We can even do the photocopy for you because of thecircumstances. S: Oh, well, that would be great. L: Isee you39。 ve got some books the one you wereasked to return? 全国免费咨询电话： 4000123267 S: No, I left it in mydorm room. These are books I need to checkout Ok if I bring that one by in a couple ofdays? L: Actually,you need to returnit today. That is if you want to checkout those books today. That39。 sour policy. S: Oh, I didn39。 t know that. L: Yeah,not a lot of people realizethat. In fact,everysemesterwe get a few studentswho have their borrowing privileges suspended pletelybecause theyhav。