『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 24 Passage 1阅读练习：Why does the author use the phrase “Note the word ‘net’” in the passage?真题题目及答案解析，TPO/Official 24 Passage 1阅读原文范文音频翻译

托福TPO/Official 24 Passage 1阅读原文Why does the author use the phrase “Note the word ‘net’” in the passage?题目答案及解析-新东方托福官方网校手机版

湖泊中的水从哪里来，水是如何离开的？

Where does the water in a lake come from, and how does water leave it?

水从流入的河流、地下水的渗水和泉水、周围土地流出的陆上水流以及直接落在湖面上的雨水进入湖泊。

Water enters a lake from inflowing rivers, from underwater seeps and springs, from overland flow off the surrounding land, and from rain falling directly on the lake surface.

水通过流出河流、渗透到湖床并蒸发而离开湖。

Water leaves a lake via outflowing rivers, by soaking into the bed of the lake, and by evaporation.

但是当考虑实际水量时，问题就变得更加复杂了：每条路线进出多少水？

The questions become more complicated when actual volumes of water are considered: how much water enters and leaves by each route?

要查明河流的输入和输出量，其实就是一个测量流入和流出河流的流量的测量的问题 。

Discovering the inputs and outputs of rivers is a matter of measuring the discharges of every inflowing and outflowing stream and river.

然后，通过找到用雨量计“有些粗略地”测量的雨水增加量和用校正其他失水源的模型测得的蒸发损失量之间的差来计算与大气的交换。

Then exchanges with the atmosphere are calculated by finding the difference between the gains from 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.

对于大多数湖泊（对于被森林包围的湖泊来说更是如此）来说，陆上水流的输入量太小，无法产生明显的影响。

For the majority of lakes, certainly those surrounded by forests, input from overland flow is too small to have a noticeable effect.

如果湖泊水位的变化有一部分是不能用河流流量加上与大气的交换来解释的，那这种变化就一定是由于从地下水渗入湖泊的水与渗入地下水的水之间的净差导致的。

Changes in lake 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.

请注意“净”一词：测量地下水流入湖泊和从湖泊中渗出的实际数量比仅推断其差异要复杂得多。

Note the word “net”: measuring the actual amounts of groundwater seepage into the lake and out of the lake is a much more complicated matter than merely inferring their difference.

一旦集齐了所有这些信息，就可以判断湖泊的流量主要是由于其表面还是地下的流入或流出导致的了。

Once all this information has been gathered, it becomes possible to judge whether a lake’s flow is mainly due to its surface inputs and outputs or to its underground inputs and outputs.

如果前者更大，则该湖泊为地表水为主的湖泊；反之，则为渗透水为主的湖泊。

If the former are greater, the lake is a surface-water-dominated lake; if the latter, it is a seepage-dominated lake.

有时，常识会告诉你这两种可能性中的哪一种适用。

Occasionally, common sense tells you which of these two possibilities applies.

例如，在丘陵国家的一个池塘中，尽管没有溪流流入，但其整个夏天都保持着稳定的水位，显然这种湖泊是以地下渗水为主的。

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 it must obviously be seepage dominated.

相反，一个池塘当中的水从其一端的小溪汇入的，而水又会从另一端流出，且这个池塘在小溪水流干涸的时候，也随之干涸，那么这个池塘则明显就是地表水补给为主的了。

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.

无论如何，一个湖是在不断地增水或流失的：它的水不只是停留在那儿，或者无论如何都不会停留很长时间。

By whatever means, a lake is constantly gaining water and losing water: its water does not just sit there, or, anyway, not for long.

这就涉及到了湖泊停留时间的问题。

This raises the matter of a lake’s residence time.

停留时间是任何特定的水分子在湖中停留的平均时间长度，其计算方法是将湖中的水量除以水从湖中流出的速率。

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.

停留时间是平均值；给定分子（如果我们能追踪其轨迹）在湖中所花费的时间取决于它所走的路线：它可能以最快、最直流的一部分流过，或者可能无限期地在死水中盘旋很久。

The residence 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.

从小型湖泊的几天到大型湖泊的数百年不等。加利福尼亚州的太浩湖有700年的停留时间。

They 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.

北美五大湖（苏必利尔湖、密歇根州、休伦湖、伊利湖和安大略湖）的停留时间分别为190年，100年，22年，2.5年和6年。

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, and 6 years.

伊利湖是停留时间 最低的：尽管它的面积比安大略湖大，但它的体积却不到安大略湖的三分之一，因为它很浅——平均不到20米。

Lake Erie’s 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 then 20 meters on average.

特定湖泊水的停留时间绝非固定时间。

A given lake’s residence time is by no means a fixed quantity.

它取决于水进入湖泊的速度，而这个速度取决于降雨量和蒸发率。

It depends on the rate at which water enters the lake, and that depends on the rainfall and the evaporation rate.

气候变化（可能是全球变暖的结果？）极大地影响了加拿大安大略省西北部一些湖泊的停留时间。

Climatic change (the result of global warming?) is dramatically affecting the residence times of some lakes in northwestern Ontario, Canada.

在1970年至1986年期间，该地区的降雨量从每年1000毫米减少到650毫米，而高于平均水平的温度加快了蒸散速率（水分通过蒸发和植物生命过程散失到大气中的速率）。

In the period 1970 to 1986, rainfall in the area decreased from 1,000 millimeters to 650 millimeters 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).

结果是，在研究期间，其中一个湖泊的停留时间从5年增加到18年。

The result has been that the residence time of one of the lakes increased from 5 to 18 years during the study period.

换水速度放慢导致一系列后果。它导致溶解的化学物质浓度越来越高，这反过来又对在此栖息的所有生物产生了显著影响。

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 he lake.

The phrase “So much” in the passage refers to

Which of the following can be inferred from paragraph 2 about the movement of water into a lake?

Why does the author use the phrase “Note the word ‘net’” in the passage?

According to paragraph 3, which of the following best describes a seepage-dominated lake?

It can be inferred from paragraph 4 that the length of time a given molecule of water remains in a lake

Why does the author discuss the Great Lakes in paragraph 5?

According to paragraph 6, which of the following explains the increase in residence time of some lakes of northwestern Ontario?

According to paragraph 6, residence time is affected by all of the following EXCEPT

Look at the four squares  that indicate where the following sentence could be added to the passage. Of course, a lake may be neither surface-water- nor seepage-dominated if, for example, its inputs are predominantly surface and its outputs are predominantly seepage.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Lake Water Where does the water in a lake come from, and how does water leave it? Water enters a lake from inflowing rivers, from underwater 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 water 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 from 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 lake 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 lake 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 lake’s 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 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 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, anyway, not for long. This raises the matter of a lake’s 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 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. They 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, and 6 years. Lake Erie’s 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 then 20 meters on average. A given lake’s residence time is by no means a fixed quantity. It depends on the rate at which water enters the lake, 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 millimeters 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 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 he lake.