托福阅读：TPO2(Desert Formation)原文及答案

　　l 段意及难句解析：

　　●第一段：

　　段意：

　　本段概述了地球沙漠化的定义与其迅速扩张的现状。

　　难句分析：

　　1. The deserts, which already occupy approximately a fourth of the Earth's land surface, have in recent decades been increasing at an alarming pace.

　　短语：at an alarming pace：以惊人速度…;

　　主干：the deserts have been increasing…;

　　释义：已经占据地球四分之一表面的沙漠，近年来正以惊人速度扩张。

　　2. The expansion of desertlike conditions

　　into areas where they did not previously exist is called desertification.

　　短语：desertlike conditions:类沙漠状况;

　　主干：the expansion of desertlike conditions is called desertification;

　　释义：本句给出沙漠化定义，即类沙漠状况向先前未出现类似情况的地区扩张的现象被称为沙漠化。

　　●第二段：

　　段意：

　　本段讲述沙漠化的主要形成原因：天然植被的丧失与接踵而来的由风蚀或水蚀作用导致的土壤腐蚀;文章接着简单描述了沙漠化的两种形成情况。

　　难句分析：

　　1. Desertification is accomplished primarily through the loss of stabilizing natural

　　vegetation and the subsequent accelerated erosion of the soil

　　by wind and water.

　　短语：stabilizing natural vegetation:固定的自然植被

　　主干：desertification is accomplished through the loss of vegetation and the erosion of soil

　　释义：即沙漠化主要A.自然原因：A1.天然植被的丧失以及接踵而来的由风蚀或水蚀作用导致的土壤腐蚀。

　　2. In some cases the loose soil is blown completely away, leaving a stony surface.

　　释义：沙漠化形成情况之一：疏松土壤被风完全吹走，留下石化表面。

　　3. In other cases, the finer particles may be removed, while the sand-sized particles are accumulated to form mobile hills or ridges of sand.

　　短语：finer particles：较细小的沙粒

　　释义：沙漠化形成情况之二：细小土壤颗粒被除去，而沙状大小的颗粒不断积累，形成可移动小沙丘或沙岗。

　　●第三段：

　　段意：

　　本段紧接上段提出的植被原因，详细描述了由于植被减少导致土壤蓄水能力下降，从而加剧水土流失，沙漠化表面逐渐形成的循环过程。

　　难句分析：

　　1. Even in the areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soil's ability to absorb substantial quantities of water.

　　短语：a soil cover:表层土壤

　　主干：the reduction of vegetation results in the loss of ability to absorb water

　　释义：即使是那些仍保留有表层土壤的区域，植被减少也通常会导致土壤蓄水能力下降，以致不能储蓄足够水量。

　　2.The impact of raindrops on the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producing a surface that allows very little water penetration.

　　短语：fine clay particles:细小的泥土颗粒;

　　water penetration:水分渗透;

　　transfer…into…:将…移动到…;

　　主干：the impact of raindrops tends to…;

　　释义：即雨水降落在疏松表土上，将性状良好的泥土颗粒移动到细小的沙间空隙中，进而将其封住，形成一种几乎不能吸收水分的表面。

　　3. The gradual drying of the soil caused by its diminished ability to absorb water results in the further loss of vegetation, so that a cycle of progressive surface deterioration is established.

　　分句：“by its diminished ability to absorb water”修饰“the gradual drying of the soil”,指出土壤干燥是由于蓄水能力下降导致的;

　　主干：the drying of the soil results in loss of vegetation,so that a cycle is established;

　　释义：即蓄水能力下降产生的土壤干燥化将导致进一步的植被流失，这样，土壤表面的渐进性腐蚀循环过程便形成了。

　　●第四段：

　　段意：

　　本段指出沙漠化加剧的另一自然原因：A2.某些地区的气候变迁----趋于更加干燥和炎热

　　难句分析：

　　1. In some regions, the increase in desert areas is occurring largely as the result of a trend toward drier climatic conditions.

　　短语：a trend toward drier climatic conditions:气候趋于干燥的趋势

　　释义：即一些地区沙漠化加剧主要是由于当地气候趋于干燥的趋势。

　　2. Continued gradual global warming has produced an increase in aridity for some areas over the past few thousand years.

　　短语：an increase in aridity：干旱的加剧

　　主干：global warming has produced an increase in aridity

　　释义：即过去几千年来，持续的全球变暖导致了一些地区干旱的加剧。

　　3. The process may be accelerated

　　in subsequent decades if global warming

　　resulting from air pollution seriously increases.

　　分句：if global warming resulting from air pullution seriously increase:条件从句，指出气候干旱趋势将会加剧的条件：如果空气污染导致的全球变暖持续不断恶化的话(if global warming

　　seriously increase)。

　　主干：the process may be accelerated if global warming increases

　　释义：如果空气污染导致的全球变暖持续不断恶化的话，气候干旱这一趋势将在近几十年内加速。

　　●第五段：

　　段意：

　　本段指出沙漠化加剧的最主要原因：B.人类活动，进而描述了B1.人口扩张导致土地产出压力过大，从而在干旱年间难以为继，沙化出现。

　　难句分析：

　　1. There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural processes rather than natural processes.

　　主干：desertification results from human activities

　　释义：本段主旨句，即大多数地区土壤沙化都是由于人类活动而非自然原因导致的。

　　2. The semiarid lands bordering the deserts exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures.

　　短语：a delicate ecological balance:脆弱的生态平衡状态

　　be limited in：在…方面能力有限

　　increased environmental pressures:加剧的环境压力

　　主干：the semiarid lands exsit in … and are limited…

　　释义：沙漠周边的半干旱土地处于脆弱的生态平衡状态中，它们适应不断增加的环境压力的能力很有限。

　　3. Expanding populations are subjecting the land to increasing pressures to provide them with food and fuel.

　　短语：expanding populations:人口增多

　　subject to:征服…使其…

　　释义：人为原因之一：人口激增导致土地必须承受提供食物和燃料的压力。

　　4. During the dry periods that are common phenomena along the desert margins, though, the pressure on the land is often far in excess of its diminished capacity, and desertification results.

　　短语：desert margins:沙漠周边地区

　　far in excess of:远远超过

　　diminished capacity:减弱的能力

　　主干：during…,the pressure is far in excess…and desertification results

　　释义：在沙漠周边经常发生的干旱时期，土地所承受的压力远远超过了它的脆弱能力，这就导致了沙漠化。