Key:
　　1．D 2．A 3．B 4．C 5．C 6．B 7．B 8．A 9．C 10．D 11．C 12．D 13．2 4 6
　　题目解析：
　　1．The word “dramatic” in the passage is closest in meaning to （Vocabulary Question）
　　A．Gradual
　　B．Complex
　　C．Visible
　　D．Striking
　　相关原句：The transition from forest to treeless tundra on a mountain slope is often a dramatic one．（Paragraph 1）
　　本题解析：dramatic意为“戏剧化的，惊人的”，与striking同义，因此选择D。
　　正确答案：D
　　2．Where is the lower timberline mentioned in paragraph 1 likely to be found?（Factual Information Question）
　　A．In an area that has little water
　　B．In an area that has little sunlight
　　C．Above a transition area
　　D．On a mountain that has on upper timberline．
　　相关原句：In many semiarid areas there is also a lower timberline where the forest passes into steppe or desert at its lower edge…（Paragraph 1）
　　本题解析：在本干旱地区树带界线1较低，即水分较少的地区会有较低的树带界线1，因此选择A。
　　正确答案：A
　　3．Which of the following can be inferred from paragraph 1 about both the upper and lower timberlines?（Inference Question）
　　A．Both are treeless zones
　　B．Both mark forest boundaries．
　　C．Both are surrounded by desert areas．
　　D．Both suffer form a lack of moisture．
　　相关原句：Within a vertical distance of just a few tens of meters, trees disappear as a life-form and are replaced by low shrubs, herbs, and grasses．This rapid zone of transition is called the upper timberline or tree line．（Paragraph 1）
　　In many semiarid areas there is also a lower timberline where the forest passes into steppe or desert at its lower edge, usually because of a lack of moisture．（Paragraph 1）
　　本题解析：无论是upper timberline还是lower timberline，它们都是树木消失的界线1，因此选择B。
　　正确答案：B
　　4．Paragraph 2 supports which of the following statements about deciduous trees?（Factual Information Question）
　　A．They cannot grow in cold climates．
　　B．They do not exist at the upper timberline．
　　C．They are less likely than evergreens to survive at the upper timberline．
　　D．They do not require as much moisture as evergreens do．
　　相关原句：Timberline trees are normally evergreens, suggesting that these have some advantage over deciduous trees (those that lose their leaves) in the extreme environments of the upper timberline．（Paragraph 2）
　　本题解析：常青树比落叶树更能适应极线1的生存环境，更容易存活（have some advantage over deciduous trees (those that lose their leaves) in the extreme environments），因此选择C。注意文中亦指出在喜马拉雅山部分地区的树带界线1处有落叶树，B错误。
　　正确答案：C
　　5．The word attain in the passage is closest in meaning to（Vocabulary Question）
　　A．require
　　B．resist
　　C．achieve
　　D．endure
　　相关原句：This is particularly true for trees in the middle and upper latitudes, which tend to attain greater heights on ridges…（Paragraph 3）
　　本题解析：attain意为“获得，得到”，此处指树木可以达到某一高度，即achieve，因此选择C。
　　正确答案：C
　　6．The word they in the passage refers to （Reference Question）
　　A．valleys
　　B．trees
　　C．heights
　　D．ridges
　　相关原句：As the snow is deeper and lasts longer in the valleys, trees tend to attain greater heights on the ridges, even though they are more exposed to high-velocity winds and poor, thin soils there．（Paragraph 3）
　　本题解析：即树木在山脊处长得更高，虽然在那里它们要经受更多考验，they指代trees，因此选择B。
　　正确答案：B
　　7．The word prone in the passage is closest in meaning to（Vocabulary Question）
　　A．adapted
　　B．likely
　　C．difficult
　　D．resistant
　　相关原句：In the tropics, the valleys appear to be more favorable because they are less prone to dry out, they have less frost, and they have deeper soils．（Paragraph 3）
　　本题解析：prone意为“有…倾向”，即“容易变得…，很可能…（likely）”，因此选择B。
　　正确答案：B
　　8．According to paragraph 3, which of the following is true of trees in the middle and upperlatitudes?
　　（Factual Information Question）
　　A．Tree growth is negatively affected by the snow cover in valleys．
　　B．Tree growth is greater in valleys than on ridges．
　　C．Tree growth on ridges is not affected by high-velocity winds．
　　D．Tree growth lasts longer in those latitudes than it does in the tropics．
　　相关原句：This is because middle- and upper- latitude timberlines are strongly influenced by the duration and depth of the snow cover．As the snow is deeper and lasts longer in the valleys, trees tend to attain greater heights on the ridges, even though they are more exposed to high-velocity winds and poor, thin soils there．（Paragraph 3）
　　本题解析：文中指出中高纬度的树木之所以在山脊处长的更高是因为山谷处的积雪太深太久，对其生长不利，所以即使山脊环境有诸多不利（风大，土壤贫瘠等），树木还是在山脊长得更高。因此选择A。
　　正确答案：A
　　9．Which of the sentences below best express the essential information in the highlighted sentence in the passage? （Sentence Simplification Question）
　　A．Because of their deformed shapes at high altitudes, trees are not likely to be seriously harmed by the strong winds typical of those altitudes．
　　B．As altitude increases, the velocity of winds increase, leading to a serious decrease in the number of trees found at high altitudes．
　　C．The deformed shapes of trees at high altitudes show that wind velocity, which increase with altitude, can cause serious hardship for trees．
　　D．Increased wind velocity at high altitudes deforms the shapes of trees, and this may cause serious stress for trees．
　　相关原句：Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes．（Paragraph 4，highlighted sentence）
　　本题解析：风速随着海拔升高而提升，并可能给树造成严重的压力，正如高海拔地区树木变形已经证明了这一点。也就是说树木变形说明了高速风对植物产生的严重压力（cause serious stress for trees），因此选择C。注意，D错误之处在于并不是变形给树造成压力，而是高速风给树造成了压力，变形只是压力的表现。
　　正确答案：C
　　10．In paragraph 4, what is the author’s main purpose in the discussion of the dramatic cessation of tree growth at the upper timberline?
　　（Rhetorical Purpose Question）
　　A．To argue that none of several environment factors that are believed to contribute to that phenomenon do in fact play a role in causing it．
　　B．To argue in support of one particular explanation of that phenomenon against several competing explanations．
　　C．To explain why the primary environmental factor responsible for that phenomenon has not yet been identified．
　　D．To present several environmental factors that may contribute to a satisfactory explanation of that phenomenon．
　　相关原句：There is still no universally agreed-on explanation for why there should be such a dramatic cessation of tree growth at the upper timberline．Various environmental factors may play a role．（Paragraph 4）
　　本题解析：作者提到树带界线1处树木的消失很惊人，是为下文讲述出现这一现象的原因(environmental factors)做铺垫，因此选择D。
　　正确答案：D
　　11．According to paragraph 6, all of the following statements are true of plants in the alpine zone EXCEPT:（Negative Factual Information Question）
　　A．Because they are low, they are less exposed to strong winds．
　　B．Because they are low, the winter snow cover gives them more protection from the extreme cold．
　　C．In the equatorial mountains, they tend to be lower than in mountains elsewhere．
　　D．Their low growth form keeps them closer to the ground, where there is more heat than further up．
　　相关原句：This enables them to avoid the worst rigors of high winds and permits them to make use of the higher temperatures immediately adjacent to the ground surface．（Paragraph 6）
　　The low growth form can also permit the plants to take advantage of the insulation provided by a winter snow cover．（Paragraph 6）
　　In the equatorial mountains the low growth form is less prevalent．（Paragraph 6）
　　本题解析：文章指出在热带地区的山上（equatorial mountains），低矮生长形态便不多见了（less prevalent），C选项却称在热带地区植物更低矮，错误，因此选择C。ABD选项内容文中都有提及。
　　正确答案：C
　　12．Look at the four squares [ █ ] that indicate where the following sentence could be added to the passage．
　　（Insert Text Question）
　　This explains how, for example, alpine cushion plants have been found growing at an altitude of 6,180 meters．
　　Where would the sentence best fit? Click on a square to add the sentence to the passage．
　　Above the tree line there is a zone that is generally called alpine tundra．█(A)Immediately adjacent to the timberline, the tundra consists of a fairly complete cover of low-lying shrubs, herbs, and grasses, while higher up the number and diversity of species decrease until there is much bare ground with occasional mosses and lichens and some prostrate cushion plants．█(B) Some plants can even survive in favorable microhabitats above the snow line．The highest plants in the world occur at around 6,100 meters on Makalu in the Himalayas．█(C) At this great height, rocks, warmed by the sun, melt small snowdrifts．█(D) This explains how, for example, alpine cushion plants have been found growing at an altitude of 6,180 meters．
　　本题解析：插入句中“this explains”和“6180 meters”与前句中“around 6100 meters”和“rocks, warmed by the sun, melt small snowdrifts（植物能存活的原因）”相呼应，插入句作为例子（for example）进一步说明了为何在高纬度植物能够存活。因此选择D。
　　正确答案：D
　　13．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．
　　（Prose Summary Question）
　　At the timberline, whether upper or lower, there is a profound change in the growth of trees and other plants．
　　●
　　●
　　●
　　Answer choices
　　1．Birch is one of the few species of tree that can survive in the extreme environments of the upper timberline．
　　2．There is no agreement among scientists as to exactly why plant growth is sharply different above and below the upper timberline．
　　3．The temperature at the upper timberline is probably more important in preventing tree growth than factors such as the amount of snowfall or the force of winds．
　　4．The geographical location of an upper timberline has an impact on both the types of trees found there and their physical characteristics．
　　5．High levels of ultraviolet light most likely play a greater role in determining tree growth at the upper timberline than do grazing animals such as the ibex．
　　6．Despite being adjacent to the timberline, the alpine tundra is an area where certain kinds of low trees can endure high winds and very low temperatures．
　　本题解析：
　　1．文中提到birch是为了说明有些阔叶树也可以在上树带界线1生长，而不是说birch是少数的能在极线1生态环境下生长的植物（“There are some areas, however, where broadleaf deciduous trees form the timberline．Species of birch, for example, may occur at the timberline in parts of the Himalayas．”第二段）。1错误。
　　2．“Various environmental factors may play a role”，“Some scientists have proposed that …”都说明对于树带界线1处植被极端变化的原因是猜测出来的。2正确。
　　3．该选项迷惑性较大。需注意选项所指的是“in preventing tree growth”，气温并不是阻止植物生长，而是“for if the growing season is too short and temperatures are too low, tree shoots and buds cannot mature sufficiently to survive the winter months”，即气温太冷加上植物不够成熟导致植物冻死。3错误。
　　4．“At the upper timberline the trees begin to become twisted and deformed．This is particularly true for trees in the middle and upper latitudes…”与“Timberline trees are normally evergreens,There are some areas, however, where broadleaf deciduous trees form the timberline…”来自于二、三两段，该两段都说明地理位置不同，树带界线1处的树木种类和形态都不同。4正确。
　　5．文中只说明紫外线强度和放牧可能是导致树带界线1处树木消失的原因，但并未指出哪一原因作用更大。5错误。
　　6．“The most striking characteristic of the plants of the alpine zone is their low growth form．This enables them to avoid the worst rigors of high winds and permits them to make use of the higher temperatures immediately adjacent to the ground surface”来自第
　　六段，该段说明了苔原环境下低矮植物能够承受恶劣环境。6正确。
　　正确答案：2，4，6