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.
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
手机泄露了你的秘密
你的手机承载着你的秘密。一项新研究发现，手机里除了存有你输入的名字和号码外，还留有你的微量DNA(脱氧核糖核酸)。
DNA(脱氧核糖核酸)是细胞里的基因物质，如同指纹，你的DNA是独一无二的——除非你是同卵双生双胞胎之一。今天科学家一般可以在犯罪现场遗留的血液、唾液、毛发中分析出DNA。分析结果经常能帮侦探识别罪犯和受害人。你的手机能透露出比你想象的要多得多的信息。
安大略省汉密尔顿McMaster大学的科学家Meghan J.McFadden听说了在一起犯罪中嫌疑人的血流到了手机上，后来还丢掉了手机。这让她想到手机上是否留下了犯罪嫌疑人的DNA——即使血不流到手机上。于是，她和纽约城市大学的同事Margaret Wallace分析了10个志愿者的翻盖手机。他们使用药签从手机的两个部位，即使用者把持的外壳，靠近使用者耳部的听筒部分，采集到了肉眼看不到的手机使用者的微量DNA。
科学家们用一种主要由酒精构成的溶液擦洗手机。擦洗的目的是去除所有易被察觉的DNA。之后，机主拿回手机使用一周。接着，研究者又把手机收回来，重复了用药签采取每部手机遗留微量DNA的步骤。
科学家们在每部手机的听筒部分都发现了DNA，从手机外壳的取样更为明显，但手机外壳的取样中还发现了那些曾摆弄过该手机的其他人的DNA.
令人称奇的是，DNA甚至出现在擦洗手机之后的药签中，这意味着清洗不会完全去掉罪犯手机上的微量DNA证据。因此，现在手机可以作为协助犯罪现场调查得出定论的线索之一。
答案：ACBDA DABAD ABBBD
第四篇 Sharks Perform a Service for Earth's Waters (A)
It is hard to get people to think of sharks as anything but a deadly enemy. They are thought to 1 people frequently. But these fish perform a 2 service for earth's waters and for human beings. Yet business and sport fishing 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 smell. It can find small amounts of substances in water, such as blood, body liquids and 9 produced by animals. These powerful 10 help sharks find 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.
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
鲨鱼有益于地球水系
要让人们相信鲨鱼不是人类的死敌不是一件容易的事。人们认为鲨鱼经常袭击人类。但鲨鱼在为地球水系和人类作着有价值的贡献。商业和捕鱼运动仍在威胁着他们的生存，有些鲨鱼面临着从地球上消失的危险。
温暖的气候影响着鱼类和鲨鱼的活动。由于水温变暖，很多鱼类游到海边。专家认为鲨鱼跟随其它鱼类，也来到人类游泳的区域。实际上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。专家还提到鲜艳的色彩和闪光的珠宝也会诱使鲨鱼袭击。
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，比如血液、体液和动物散发的化学物质。灵敏的嗅觉有助于鲨鱼找到食物。鲨鱼以鱼、其他鲨鱼和海洋植物为生。
医学研究人员想要更多了解的是鲨鱼的身体抗病免疫系统。研究人员发现鲨鱼受伤会很快康复，他们希望通过研究鲨鱼，找到一种人类抗病的方法。
鲨鱼有益于海洋。它们吃受伤的和生病的鱼。他们的捕猎活动使其它海洋鱼类的数目不会过多，这就保护了海洋中的植物和其它生灵。
答案：ACBDC DBACB DAABD
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