An avalanche is a sudden and rapid flow of snow, often mixed with air and water, down a mountainside. Avalanches are 1 the biggest dangers in the mountains for both life and property.
All avalanches are caused by an over=burden of material, typically snowpack, that is too massive and unstable for the slope 2 supports it. Determining the critical load, the amount of over-burden which is 3 to cause an avalanche, 4 a complex task involving the evaluation of a number of factors.
Terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low 5 of avalanche. Snow does not 6 significantly on steep slopes; also, snow does not 7 easily on fiat slopes. Human-triggered avalanches have the greatest incidence when the snow's angle of rest 1is 8 35 and 45 degrees; the critical angle, the angle at which the human incidence of avalanches is greatest, is 38 degrees. The rule of thumb2 is: A slope that is 9 enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. Additionally3, avalanche risk increases with 10 ; that is, the more a slope is disturbed by skiers, the more likely it is that an avalanche will occur.
Due to the complexity of the subject, winter travelling in the backcountry4 is never 100% safe. Good avalanche safety is a continuous 11 , including route selection and examination to the snowpack, weather 12 , and human factors. Several well-known good habits can also 13 the risk. If local authorities issue avalanche risk reports, they should be considered and all warnings should be paid 14 to. Never follow in the tracks of others without your own
evaluations; snow conditions are almost certain to have changed since they were made. Observe the terrain and note obvious avalanche paths where plants are 15 or damaged. Avoid traveling below others who might trigger an avalanche.
词汇：
avalanche n.雪崩 trigger v. 引起，激发
snowpack n. 积雪场 incidence n.发生(率)
terrain n. 地形，地势 ski v.滑雪
steep adj.险峻的，陡峭的 complexity n. 复杂性
注释:
1.angle of rest：这里指积雪保持静止的角度。
2.rule of.thumb：指“a broadly accurate principle，based on experience or practice rather that theory”，即“通用法则，经验法则”。
3.Additionally：是一个副词，用来引人新的事实或论点，意为“此外”。
4.backcountry：人烟稀少的地区。
练习:
1. A among B of C to D in
2. A when B that C who D whose
3. A mostly B likely C clearly D surely
4. A are B will be C is D was
5. A weight B form C risk D work
6. A fall B flow C roll D gather
7. A fall B flow C roll D gather
8. A among B between C with D for
9. A thick B thin C flat D rocky
10. A use B time C snow D rain
11. A journey B trip C fact D process
12. A conditions B reports C forecast D event
13. A increase B reduce C improve D remove
14. A price B effort C attention D money
15. A missing B grown C big D fresh
答案与题解：
1.A表达“雪崩是山上可能发生的最大危险之一”的意思，因此应该选择among(在……之中)。
2.B从该句的语法结构上来看，此处需要一个关系代词，代替slope，所以that是最佳选择。选项A、C、D均不符合语法。
3.B选项A不符合语法，c和D符合语法，但不符合常识：过度的雪的积压可能导致雪崩，
而不是必定导致雪崩。所以，B是最佳答案。
4.C该句的主语是Determining the critical load，从上下文来看应该使用一般现在时，所以C是正确答案。
5.C要确定本题答案的一个有效的方法是排除法。a.10w weight/form work of avalanche都不合逻辑，只有a low risk of avalanche符合上下文的意思。下面的句子解释了low risk of avalanche的道理，更证实了选risk是正确的。
6.D第6和第7题可以一起考虑。整个句子的意思是：在坡度大的坡上，雪不会大量堆积。
在较为平坦的坡面，雪不会轻易滑动。
7.B(见6)
8.B理解了句子的意思就不难判断选项：雪在静止状态下，角度在35_45度之间，最可能发生人为触发的雪崩。between：在……之间。
9.C这个句子说明的是什么样的山坡最易发生雪崩，即，A slope that is flat enough to hold snow but steep enough to ski。flat在此做“平坦”解，与后面的steep形成反义。
10.A句中的that is表明，后半部分是对前半部分的进一步说明。所以，这里的选择要根据下文的意思判断。use是最佳选择，整个句子的意思是：山坡被滑雪者使用的越多，雪崩就越可能发生。 、
11.D尽管选项A、B和D都能和continuous搭配，从全段的内容判断，只有process是最佳选择，因为该段描写的是如何防备雪崩，及如何做好安全措施等一系列问题。
12.A选项A、B、c都可以与weather搭配，但是根据上下文，只有A最为符合文章的内容。
13.B选项A不符合句子的意思;c不能和risk搭配;D也不符合句子的意思，因为不可能完全消除雪崩的隐患。
14.C该句主句使用的是被动语态，第二个动词是pay attention t0的被动形式。l选项A、B、D均不符合句子的意思。
15.A该句是作者给出的一系列忠告之一，即，认真观察地形，注意明显的雪崩路径：没有植物或植物被毁坏的地方。选项8、C、D均不符合句义。
Taking a Nap During the Day
Medical experts say most Americans do not get 1 sleep. They say more Americans need to rest for a short period in the middle of the day. They are advising people to sleep lightly before 2 with other activities.
One study earlier this year found that persons who sleep for a few minutes during the day were less 3 to die of disease. The study followed more than 2,300 Greek adults 4 about six years. Adult who rested for half an hour 5 three times a week had a 37 percent lower risk of dying from heart disease than those who did not nap.
Study organizers said the strongest evidence was in working men. They said naps might improve 6 by mitigating tension caused by work.
Some European and Latin American businesses have supported the 7 of napping for many years. They urge people to 8 work, go home and have a nap before returning. In the United States, some companies let workers rest briefly in their offices. They believe this reduces in their offices. They believe this reduces 9 and accidents, and 10 increases the amount of work a person can do.
Sleep experts say it is likely that people make more mistakes at work than at other times1. They say people should not carry out important duties when they feel 11 . And they say the best thing to do is to take a nap. About twenty minutes of rest is 12 you need. Experts say this provides extra energy and can increase your effectiveness 13 the end of the day. But experts warn that a nap 14 last no more than twenty to thirty minutes. A longer nap will put the body into deep sleep2 and waking up3 will be 15
词汇:
Nap n. 打盹 mitigate v.减价
urge v.催促，劝告
注释:
1.people make more mistakes at work than at other times：人们在工作(时间)中出错的概率比其它的时间要多。本句中的at work可以理解为during their work time。
2.put…into deep sleep：使……进人深睡状态
3.waking up：从上下文判断，waking up是“自己醒过来”的意思，不是“唤醒”。
练习:
1. A sweet B sound C bad D enough
2. A checking B sharing C continuing D meeting
3. A lovely B likely C fondly D finely
4. A for B at C in D with
5. A at least B at most C at last D at first
6. A ability B health C thinking D life
7. A experiment B reform C idea D way
8. A repeat B improve C change D leave
9. A work B mistakes C energy D time
10. A never B seldom C too D also
11. A ready B good C sleepy D awake
12. A all B few C any D nothing
13. A unless B while C until D during
14. A would B may C might D should
15. A helpful B difficult C easy D happy
答案与题解:
1.D本段第二句说“more Americans need to rest for a short period in the middle of the day”。引导我们选择(not)enough。因为睡眠不够，才要中午“打个盹”。选项A：文不对题。选项B：bad(sleep)与上下文不符，因为通篇文章没有提到过，中午打盹的原因是晚上没有睡好。选项C：明显不合乎逻辑。“由于没有睡不好(即：晚上睡好了)，白天还要补睡一会儿”，于理说不通。所以，惟一合理的选择是enough。 ’
2.C空格2所在句子的意思是：医学专家建议人们在进行其它活动之前，最好小睡一会。四个选项中，只有continuing(选项C)最接近上述的理解。
3.B空格3所在的句子说的是“心脏病致死”的问题，lovely，fondly和finely分别表达“可爱”、“喜欢”和“美好”的意思，明显不对。less likely是“可能性较低一些”的意思，选择likely符合上下文的意思。本段最后一句说，成年人白天打盹半小时，一周三次，其心脏病致死的概率比不打盹的人要低37%。这更证实了选likely是正确的。
4.A本句的意思是，调查进行了六年。about six years之前要用表达一段时间的介词for。介词at和with明显与about six years不搭配，而选项in(about six years)表达的是未来的时间，如：He will come to Beijing in one day or tw0.(他一、两天之内会到北京。)
5.A at first和at last明显与本句的意思不符。若选at most(最多)，本句的意思成了“成年人白天打盹半小时，一周不得超过三次，其心脏病致死的概率比不打盹的人要低37%”，意思有点令人费解。改说成，“一周至少三次”才说得通。所以at least是答案。
6.B通篇文章在阐述白天打盹有益于健康，选项B是答案。
7.C空格7所在的句子的意思是：多年来，欧洲和拉丁美洲的一些公司支持白天打盹的 ? (空格中填哪一个词?)。很明显，空格中填入experiment(试验)或reform(改革)则离题太远，而way(方式)肯定没有idea(想法)好。C是答案。
8.D从上下文判断，空格8的词应该与“中止(work)”有关。四个选项中，只有leave合乎这一条件。而其它三个选项repeat(重复)、improve(改进)和change(改变)与后半句的go home and have a nap搭不上。
9.B前面一句说，美国有些公司让职员在办公室打个盹，这样可以减少些事故等。填人空格9的词应该与accidents(事故)一样，是一个负面意思的词。mistakes(选项B)符合这个条件，是答案。reduce work/energy time都不合理。
10.D 打个盹有两个好处：1)可以减少错误和事故;2)可以增加工作效率。从上下文判断，
选als0最合适。t00从词义上说也可以，但用法上有问题，因为“…this…too increases the amount…”把t00置于动词increases之前很少见。never和seldom的意思与上下文不匹配。
11.C前半句说，“people should not carry out important dudes…”，后半句自然会想到“when they feel sleepy”。而when they feel ready good happy都说不通。
12.A本句的意思是：大约20分钟的打盹是你所需要的。所以，About twenty minutes of rest is few/any/nothing you need与上述意思不符，只有About twenty minutes of rest is all you need才说得通。
13.C前半句说，“this(指打肫)provides extra energy and Can increase your effectiveness”后面接while unless during the end of the day不搭配，只有until(the end of the day)才是答案。
14.D本句的意思是：专家警告说：打盹不能(或不应该)超过30分钟。这题选should最合适。
15.B本句表达的意思应该是上一句“A longer nap will put the body into deep sleep”引出的结果。打盹时间长了，就会进入深睡状态，很难醒过来。选difficult是合适的，其它三个选项的意思脱离了上下文，不会是答案。
Cell Phone Lets Your Secret Out
Your cell phone holds secrets about you. Besides the names and 1 that you've programmed into it, traces of your DNA2linger on the device, according to a new study.
DNA is genetic material that 2 in every cell. Like your fingerprint, your DNA is unique to you 3 you have an identical twin. Scientists today routinely analyze DNA in blood, saliva, or hair left 4 at the scene of a crime. The results often help detectives identify 5 and their victims. Your cell phone can reveal more about you 6 you might think.
Meghan J. McFadden, a scientist at McMaster University1in Hamilton, Ontario, heard about a crime in which the suspect bled onto a cell phone and later dropped the 7 This made her wonder whether traces of DNA lingered on cell phones--even when no blood was involved. 8 she and colleague Margaret Wallace of the City University of New York analyzed the flip-open phones3 of 10 volunteers. They used swabs to collect 9 traces of the users from two parts of the phone: the outside, where the user holds it, and the 10 , which is placed at the user's ear.
The scientists scrubbed the phones using a solution made mostly 11 alcohol. The aim of washing was to remove all detectable traces of DNA. The owners got their phones 12 for another week. Then the researchers collected the phones and repeated the swabbing of each phone once more.
The scientists discovered DNA that 13 to the phone's speaker on each of the phones. Better samples were collected from the outside of each phone, but those swabs also picked up DNA that belonged to other people who had apparently also handled the phone. 14 , DNA showed up even in swabs that were taken immediately after the phones were scrubbed. That suggests that washing won't remove all traces of evidence from a criminal's device. So cell phones can now be added to the 15 of clues that can clinch a crime-scene investigation.
词汇:
linger v.逗留 flip-open phone 翻盖手机
genetic adj.遗传的 swab n. 药签
saliva n. 涎，唾液 scrub v. 用力擦洗;擦净
bleed v. 流血 clinch v.确定，决定
注释:
1.McMaster University：麦克马斯特大学，位于加拿大安大略省汉密尔顿市，成立于1887年。
2.DNA：脱氧核糖核酸。系deoxyribonucleic acid的缩写。 .
3.flip—open phones：翻盖手机。又可作flip phones。
练习：
1. A numbers B music C secrets D films
2. A appeals B appoint C appears D applies
3. A because B unless C although D still
4. A about B in C for D behind
5. A criminals B people C men D policemen
6. A when B until C before D than
7. A device B paper C file D document
8. A However B So C But D Nevertheless
9. A invisible B non-existent C visible D apparent
10. A card B keys C screen D speaker
11. A of B up C on D into
12. A upon B back C without D with
13. A was given B belonged C was owned D became
14. A Generally B Surprisingly C Disappointedly D Shortly
15. A explanation B discovery C book D list
答案与解析：
1.A人们通常在手机中储存人名和他们的电话号码。所以A是最佳选择。虽然手机中也能储存音乐和秘密信息，相比之下，不如A合理。至于储存电影片子，就有点离谱了。
2.C这个句子的意思是：DNA是一种存在于每一细胞中的基因物质。根据这一理解，选项A、B、D均不能选作答案。
3.B上文的意思是：如同指纹，你的DNA是独一无二的。因此，此处必须选择unless，其他选择均不符合句义，也违背了我们对DNA的基本常识。 4.D leave behind是固定搭配，意即：留下。此处leave使用的是过去分词形式。
5.A根据上下文的理解，研究结果是用来帮助侦探识别罪犯和受害人的，8、c、D都不能表
达这一层意思。
6.D句子中的more提供了选择的线索，more…than的搭配最能完成该句的意思。
7.A定冠词the说明该选项所指内容在前面已经提到，即cell phone。除了device，其他选项均不能指代cell phone。
8.B 四个选项中只有B是正确选择。s0连接了其前后两个句子，使其形成因果关系：她思考微量DNA是否会停留在手机上，所以，她与同事们一起对10名志愿者的翻盖手机进行了分析研究。A、C、D表示的都是转折的意义关系。
9.A句子当中的paces指的是DNA traces(微量DNA)，而DNA paces是肉眼看不到的，所
以选择invisible。
10.D研究者从手机的两部分收集手机微量DNA：一是手机外壳，二是喇叭。贴在耳朵上的
不可能是card、screen和keys。
11.A be made of是固定搭配，意即：由…制成。a solution made mostly of alcohol：一种主要由酒精制成的溶液。
12.B根据上下文的理解，应该选择back：手机拥有者拿回了手机，再使用一个星期。
13.B 该句要表达的意思应该是：科学家在每一个手机上发现了属于手机拥有者的DNA。
belong t0是固定搭配，意思是：属于。A不符合句义，c和D不符合语法。
14.B最后一段的第一和第二句告诉我们手机经过清洗后仍然有微量DNA出现。所以这里
要用surprisingly这个副词，表示令人惊讶。
15.D根据上下文的理解，应该选择D，其它三个选项与句子的意思不符。
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 to 1 people frequently. But these fish2 perform a 2 service for earth's waters and for human beings. Yet business and sport fishing3 are threatening their 3 Some sharks are at risk of disappearing from 4
Warm weather may influence both fish and shark activity. Many fish swim near coastal areas 5 their warm waters. Experts say sharks may follow the fish into the same areas, 6 people also swim. In fact, most sharks do not purposely charge at or bite humans. They are thought to mistake a person 7 a 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 the 8 when 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 and 9 produced by animals. These powerful 10 help sharks fred their food. Sharks eat fish, any 11 sharks, and plants that live in the ocean.
Medical researchers want to learn more about the shark's body defense, and immune 12 against disease. Researchers know that sharks 13 quickly from injuries. They study the shark in hopes of finding a way to fight human disease.
Sharks are important for the world's 14 They eat injured and diseased fish. Their hunting activities mean that the numbers of other fish in ocean waters do not become too 15 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:
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。