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Sharks Perform a Service for Earth's Waters

It is hard to get people to think of sharks as anything but a deadly enemy1.They are thought to1people frequently.But these fish2 perform a2service for earth's waters and for human beings.Yet business and sport fishing3 are threatening their3Some sharks are at risk of disappearing from 4

Warm weather may influence both fish and shark activity.Many fish swim near coastal areas5their warm waters.Experts say sharks may follow the fish into the same areas,6people also swim.In fact,most sharks do not purposely charge at or bite humans.They are thought to mistake a person7a sea animal,such as a seal or sea lion.That is why people should not swim in the ocean when the sun goes down or comes up.Those are the8when sharks are looking for food.Experts also say that bright colors and shiny jewelry may cause sharks to attack.

A shark has an extremely good sense of smell4' It can find small amounts of substances in water,such as blood,body liquids and9produced by animals.These powerful10help sharks fred their food.Sharks eat fish,any11 sharks,and plants that live in the ocean.

Medical researchers want to learn more about the shark's body defense,and immune12against disease.Researchers know that sharks13quickly from injuries.They study the shark in hopes of finding a way to fight human disease.

Sharks are important for the world's14They eat injured and diseased fish.Their hunting activities mean that the numbers of other fish in ocean waters do not become too15.This protects the plants and other forms of life that exist in the oceans.

词汇：

purposely adv.故意地，蓄意地 immune adj.免疫的

charge v.（向）冲（过去） jewelry n.珠宝

seal n.海豹

注释：

1.It is hard to get people tO think of sharks as anything but a deadly enemy：要让人们相信鲨鱼不是

（人类的）死敌不是一件容易的事。anything but意为“决不，远非'，如：His performance in London is anything but a success.（她在伦敦的演出完全不成功。）

2.these fish：这些鱼（指鲨鱼）。fish单复数同形，如：0ne fish，two fish，many fish（见第二段第一句）。

3.sport fishin9：捕鱼运动。

4.sense of smell：嗅觉

练习：

1.A attack B meet C love D visit

2.A terrible B eatable C valuable D possible

3.A source B existence C friends D fish

4.A Space B Sky C Land D Earth

5.A because B since C because of D by reason that

6.A whose B which C that D where

7.A to B for C like D with

8.A times B places C seas D oceans

9.A sciences B mathematics C chemicals D physics

10.A feelings B senses C touches D tastes

11.A those B these C another D other

12.A systems B processes C ideas D circles

13.A recover B reform C return D rely

14.A rivers B oceans C forests D mountains

15.A weak B little C few D great

答案与题解：

1.A本题应选择attack，因为第一句说到：人们认为鲨鱼是a deadly enemy，也就是说鲨鱼会对人类造成伤害。第二句是对deadly enemy的具体说明。其他的三个选项meet，love，visit都不合适，love与上下文意思相反，meet和visit与上下文意思不符。

2.C空格2所在的句子由but连接，所以该句子表达的意思一定与第二句相反。第二句对鲨鱼的评价是负面的，填入空格2的词应该是正面的。四个选项中只有valuable符合这一条件，所以是答案。

3.B第三句说到鲨鱼有益于“waters and human beings'，第五句又说到鲨鱼濒临灭绝的危险。根据上下文的意思，threatening（威胁）到它们的应该是existence（生存）。其他的三个选项source，friends，fish都不合适，与上下文意思没有联系。

4.D如果鲨鱼消失，从什么地方消失呢？当然从earth（地球）上消失。从space（宇宙空间）、sky（天空）中消失，或从land（陆地）上消失，都有悖常理。

5.C四个选项的意思都是“因为'，但是从用法上分析，because、since和by reason that之后要接句子，because of之后接名词或名词短语。their warm waters是名词短语，所以要选用because of.

6.D“？people also swim'明显是定语从句，其先行词是表示地点的名词area，所以要选关系副词where.。

7.B从上下文判断，本句的意思是：鲨鱼将人错认为是海洋动物。而“将？？错认为是'的英语表达是mistake？for，所以本题的答案是选项B.

8.A本段的意思是：鲨鱼并非故意袭击人类。人们认为，由于鲨鱼将人错认为是海狮等海洋动物，在饥饿时才袭击人类。日出和日落时，正是鲨鱼饥肠辘辘的时候，人们不应该出海游泳。空格8填入的词应该与时间有关，所以times是答案，而与地点有关的选项（places seas和oceans）与上下文意思脱节。

9.C本段第一、二句是说，鲨鱼的嗅觉特别灵敏，能嗅到海水中存在的极为微量的气味。作者举了三个物质：血、体液和化学品。空格9要填入表示物质的名词。四个选项中惟一表达物质的词是chemicals（化学品）。所以chemicals是答案，而其它三个选项与学科有关，脱离了上下文的意思，不是本题的答案。

10.B在第一、二句意思的基础上，作者进一步说明，灵敏的嗅觉有助于鲨鱼找到食物。所以本题的答案是选项D的senses，因为feelings，touches和tastes都与smells无关。

11.D 本句的中心词是复数的sharks，another所修饰的名词一般是单数，所以不会是答案。these和those是表特指的代词，指代前面出现过的名词。由于前面没有先行词，所以也不可能是答案。剩下的other是答案，any other sharks的说法也合乎英语的用法。

12.A从上下文判断，医学研究人员想要更多了解的是“身体抗病system（系统）'，不会是“身体抗病idea（思想）'、“身体抗病工作（work）'或“身体抗病circle（周期）'。

13.A本段最后一句的意思是：医学研究人员研究鲨鱼的目的是为了找到一种人类抗病的方法。所以空格l3所在句子的意思应该是recover（quickly from injuries）。科学家想要探索的应该是有关受伤鲨鱼recover quickly from injuries的秘密，而reform（改造）、return（回归）和rely（依靠）只是与答案recover词形上有点相似而已，其意思与上下文的意思风马牛不相及。

14.B 从上下文判断，鲨鱼的存在能使0ceans得益。鲨鱼不生活在rivers、forests或mountains中，所以，这三个选项不会是答案。

15.D本段的其余三句都是说明为什么鲨鱼有益于海洋。它们吃海洋动物，结果使得海洋中的动物数量不会过多。weak、little、few都与上面表达的意思相反，所以，只有great是答案。