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1、以下，是这次环球托福为正在进行托福备考的考友们整理了托福 TPO24 阅读真题及答案 Lake Water。我们建议考友们，先做真题，后看答案进行验证自己的正确率。之后，环球托福还会进一步推出托福 TPO24 阅读真题的做题思路讲解分析，做完真题后，更便于提高托福阅读能力。托福 TPO24 阅读真题 Lake WaterLake WaterWhere does the water in a lake come from, and how does water leave it? Water enters a lake from inflowing rivers, from underwater
2、 seeps and springs, from overland flow off the surrounding land, and from rain falling directly on the lake surface. Water leaves a lake via outflowing rivers, by soaking into the bed of the lake, and by evaporation. So much is obvious.The questions become more complicated when actual volumes of wat
3、er are considered: how much water enters and leaves by each route? Discovering the inputs and outputs of rivers is a matter of measuring the discharges of every inflowing and outflowing stream and river. Then exchanges with the atmosphere are calculated by finding the difference between the gains fr
4、om rain, as measured (rather roughly) by rain gauges and the losses by evaporation, measured with models that correct for the other sources of water loss. For the majority of lakes, certainly those surrounded by forests, input from overland flow is too small to have a noticeable effect. Changes in l
5、ake level not explained by river flows plus exchanges with the atmosphere must be due to the net difference between what seeps into the lake from the groundwater and what leaks into the groundwater. Note the word net: measuring the actual amounts of groundwater seepage into the lake and out of the l
6、ake is a much more complicated matter than merely inferring their difference.Once all this information has been gathered, it becomes possible to judge whether a lakes flow is mainly due to its surface inputs and outputs or to its underground inputs and outputs. If the former are greater, the lake is
7、 a surface-water-dominated lake; if the latter, it is a seepage-dominated lake. Occasionally, common sense tells you which of these two possibilities applies. For example, a pond in hilly country that maintains a steady water level all through a dry summer in spite of having no streams flowing into
8、it must obviously be seepage dominated. Conversely, a pond with a stream flowing in one end and out the other, which dries up when the stream dries up, is clearly surface water dominated.By whatever means, a lake is constantly gaining water and losing water: its water does not just sit there, or, an
9、yway, not for long. This raises the matter of a lakes residence time. The residence time is the average length of time that any particular molecule of water remains in the lake, and it is calculated by dividing the volume of water in the lake by the rate at which water leaves the lake. The residence
10、 time is an average; the time spent in the lake by a given molecule (if we could follow its fate) would depend on the route it took: it might flow through as part of the fastest, most direct current, or it might circle in a backwater for an indefinitely long time.Residence times vary enormously. The
11、y range from a few days for small lakes up to several hundred years for large ones; Lake Tahoe, in California, has a residence time of 700 years. The residence times for the Great Lakes of North America, namely, Lakes Superior, Michigan, Huron, Erie, and Ontario, are, respectively, 190,100,22,2.5, a
12、nd 6 years. Lake Eries is the lowest: although its area is larger than Lake Ontario s, its volume is less than one-third as great because it is so shallow-less than 20 meters on average.A given lakes residence time is by no means a fixed quantity. It depends on the rate at which water enters the lak
13、e, and that depends on the rainfall and the evaporation rate. Climatic change (the result of global warming?) is dramatically affecting the residence times of some lakes in northwestern Ontario, Canada. In the period 1970 to 1986, rainfall in the area decreased from 1,000 millimeters to 650 millimet
14、ers per annum, while above-average temperatures speeded up the evapotranspiration rate (the rate at which water is lost to the atmosphere through evaporation and the processes of plant life).The result has been that the residence time of one of the lakes increased from 5 to 18 years during the study
15、 period. The slowing down of water renewal leads to a chain of further consequences; it causes dissolved chemicals to become increasingly concentrated, and this, in turn, has a marked effect on all living things in the lake.托福 TPO24 阅读真题 Lake Water 题目1. The phrase So much in the passage refers toA.t
16、he negative effects of overland flow, rain, and evaporation on river water levelsB.water that a lake loses to outflowing rivers, to the lake bed, and to evaporationC.the importance of rivers to the maintenance of lake water levelsD.the information given about ways that water can enter or exit a lake2. The word gains in the passage is closest in meaning toA.resultsB.increasesC.resourcesD.savings3. Which of the following can be inferred from paragraph 2 about the movement of water i
