the colour of the oceans would occur. The model projects that currently blue areas with little phytoplanton could become even bluer. But in some waters，such as those of the Arctic，a warming will mae conditions riper for phytoplanton，and these areas will turn greener. “Not only are the quantities of phytoplanton in the ocean changing. ”she said，“but the type of phytoplanton is changing. ” 42. What are the first two paragraphs mainly about? A. The various patterns at the ocean surface. B. The cause of the changes in ocean colour. C. The way light reflects off marine organisms. D. The efforts to fuel the growth of phytoplanton.

43. What does the underlined word“vulnerable”in Paragraph 3 probably mean? A. Sensitive.

B. Beneficial

C. Significant

D. Unnoticeable

44. What can we learn from the passage?

A. Phytoplanton play a declining role in the marine ecosystem. B. Dutiewic's model aims to project phytoplanton changes C. Phytoplanton have been used to control global climate D. Oceans with more phytoplanton may appear greener. 45. What is the main purpose of the passage？

A. To assess the consequences of ocean colour changes B. To analyse the composition of the ocean food chain C. To eplain the effects of climate change on oceans D. To introduce a new method to study phytoplanton

【语篇解读】本文为说明文。一项最新研究表明，由于气候变暖，世界海洋将会变得更蓝、更绿。这一现象是因为一种叫做浮游植物的微小海洋微生物，因为光线反射的作用，它们在海洋表面形成了五颜六色的图案。但是浮游植物很容易受到海洋变暖趋势的影响。气候变暖会改变海洋的主要特征，并影响浮游植物的生长。 42. B

【解析】段落大意题。第一段“By the end of the century. If not sooner, the world's oceans will be bluer and greener thans to a warming climate, according to a new study.”可知，到本世纪末，一项新的研究表明，由于气候变暖，如果不尽快的话，世界上的海洋将会变得更蓝、更绿。结合第二段“At the heart phenomenon lie tiny marine microorganisms called phytoplanton. Becaust of the way light reflects off the organisms ,these phytoplantons create

colourful patterns at the ocean surface. Ocean colour varies from green to blue, depending on the type and concentration”可知，这种现象的核心是一种叫做浮游植物的微小海洋微生物，在光线的作用下在海洋表面形成了五颜六色的图案。海洋的颜色从绿色到蓝色不等，这取决于海洋的类型和浮游植物浓度。由此可推断出这两段主要叙述了海洋生物是海洋颜色变化的原因。分析选项可知B符合题意，故选B。 43. A

【解析】词义猜测题。根据划线词后的“Warming changes ey characteristics of the ocean and can affect phytoplanton growth, since they need not only sunshine and carbon dioide to grow, but also nutrients.”可知，气候变暖会改变海洋的主要特征，并会影响浮游植物的生长。由此可判断“But phytoplanton are vulnerable to the ocean’s wamning trend”可知，浮游植物很容易受到海洋变暖趋势的影响。可知A项正确。 44. D

【解析】推理判断题。根据第四段“The model projects that currently blue areas with little phytoplanton could become even bluer. But in some waters ,such as those of the Arctic, a warming will mae conditions riper for phytoplanton, and these areas will turn greener”,可知Dutiewic的模型预测，目前只有少量浮游植物的蓝色区域可能会变得更蓝。但是在一些水域，比如北极，气候变暖会使浮游植物的生长条件更加成熟，而这些水域会变得更绿了”。由此可推断，浮游植物的生长条件更加成熟，浮游动植物就更多了，这些水域会变得更绿了。分析选项可知D项符合题意。 45. C

【解析】目的意图题。第一段提出文章的主旨“By the end of the century. If not sooner, the world's oceans will be bluer and greener thans to a warming climate, according to a new study.”可知到本世纪末。一项新的研究表明，由于气候变暖，如果不尽快的话，世界上的海洋将会变得更蓝、更绿。再结合第三段“But phytoplanton are vulnerable to the ocean’s warning trendWarming changes ey characteristics of the ocean and can affect phytoplanton growth, …”可知，“浮游植物很容易受到海洋警告趋势的影响，变暖改变了海洋的关键特征，并能影响浮游植物的生长”。可知本文主要解释气候变化对海洋的影响。故选C。 8. 【2019·天津卷，C】

How does an ecosystemwor？What maes the populations of different species the way they are？（生态系统）Why are there so many flies and so few wolves？To find an answer，scientists have built mathematical models of food webs，noting who eats whom and how much each one eats.

With such models，scientists have found out some ey principles operating in food webs. Most food webs，for instance，consist of many wea lins rather than a few strong ones. When a predator（掠食动物）always eats huge numbers of a single preythe two species are strongly lined；when a predator lives on various species，they （猎物），

are wealy lined. Food webs may be dominated by many wea lins because that arrangement is more stable over the long term. If a predator can eat several species，it can survive the etinctionof one of them. And if a predator （灭绝）can move on to another species that is easier to find when a prey species becomes rare，the switch allows the original prey to recover. The wea lins may thus eep species from driving one another to etinction.

Mathematical models have also revealed that food webs may be unstable，where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s，scientists proposed that predators at the top of a food web had a surprising amount of control over the sie of populations of other species---including species they did not directly attac.

And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean，we fished for top predators such as cod on an industrial scale，while on land，we illed off large predators such as wolves. These actions have greatly affected the ecological balance.

Scientists have built an early-warning system based on mathematical models. Ideally，the system would tell us when to adapt human activities that are pushing an ecosystem toward a breadown or would even allow us to pull an ecosystem bac from the borderline. Prevention is ey，scientists says because once ecosystems pass their tipping point（临界点），it is remarably difficult for them to return.

46. What have scientists discovered with the help of mathematical models of food webs？ A. The living habits of species in food webs. B. The rules governing food webs of the ecosystems. C. The approaches to studying the species in the ecosystems. D. The differences between wea and strong lins in food webs. 47. A strong lin is found between two species when a predator______ A. has a wide food choice B. can easily find new prey C. stics to one prey species D. can quicly move to another place

48. What will happen if the populations of top predators in a food web greatly decline？ A. The prey species they directly attac will die out.

B. The species they indirectly attac will turn into top predators. C. The living environment of other species will remain unchanged. D. The populations of other species will eperience unepected changes.

49. What conclusion can be drawn from the eamples in Paragraph 4？ A. Uncontrolled human activities greatly upset ecosystems. B. Rapid economic development threatens animal habitats. C. Species of commercial value dominate other species. D. Industrial activities help eep food webs stable.

50. How does an early-warning system help us maintain the ecological balance？ A. By getting illegal practices under control. B. By stopping us from illing large predators.

C. By bringing the broen-down ecosystems bac to normal. D. By signaling the urgent need for taing preventive action.

【语篇解读】这是一篇说明文。本文介绍了借助食物网的数学模型，科学家们发现了一些在食物网运营的关键原则。科学家们说;因为一个生态系统越过了它的临界点，它们很难再回。该系统将告诉我们何时 适应人类活动，这些活动正将生态系统推向崩溃，或者甚至允许我们将生态系统从边缘拉回，预防是关键。46.B

【解析】细节理解题。根据第一段的With such models, scientists have found out some ey principles operating in food webs.可知，借助食物网的数学模型，科学家们发现了食物网中的一些关键原则。故选B。 47. C

【解析】细节理解题。根据第一段的When a predator(掠食动物) always eats huge numbers of a single prey(猎物)，the two species are strongly lined可知，当捕食者总是吃大量的单一猎物，这两个物种是紧密相连的。故选C。 48. D

【解析】推理判断题。根据第二段的In the 1960s, scientists proposed that predators at the top of a food web had, a surprising amount of control over the sie of populations of other species they did not directly attac可知，处于食物网顶端的食肉动物对它们没有直接攻击的其他物种的种群数量有着惊人的控制，由此可推断出，如果食物链顶级食肉动物的数量大大下降，其他物种的种群将经历意想不到的变化。故选D。 49.A

【解析】推理判断题。根据第四段的Ideally the system would tell us when to adapt human activities that are pushing an ecosystem toward a breadown or would even allow us to pull an ecosystem bac from the borderline可知，人类过度的活动会将生态系统推向崩溃，由此可推断出，不受控制的人类活动极大地破坏了生态系统。故选A。