题目内容
7．Elephants have impressed us for centuries．They are big，clever，and sociable．But what if someone told you that they may also hold the key to fighting cancer？People have been wondering why elephants do not develop cancer，even though they have life spans（寿命）that are similar to humans，living for around 50to 70years．
Now scientists believe they know why．A team at the University of Chicago，Us has found that elephants carry a large number of genes that stop tumors（肿瘤）from developing．To be precise，they found 20copies of an anti-tumor gene called TP 53in elephants．Most other species，humans included，only carry one copy．
According to the research，which was recently published on the online science network BioRxiv，the extra copies of the gene improved the animal's sensitivity to DNA damage．This lets the cells（细胞）quickly kill themselves when damaged before they can form deadly tumors．
"An increased risk of developing cancer has stood in the way of the evolution of large body sizes in many animals，"study author Dr Vincent Lynch told The Guardian．If every living cell has the same chance of becoming cancerous，large creatures with long life spans like whales and elephants should have a greater risk of developing cancer than humans and mice do．But across species，the risk of cancer does not show a connection with body mass．
This phenomenon was found by Oxford University scientist Richard Peto in the 1970s and later named"Peto's paradox"．Evolutionary biologists believe it results from larger animals using protection that many smaller do not，In the elephant's case，the making of TP53is nature's way of keeping this species alive．
The study also found that when the same genes were brought to life in mice，they had the same cancer resistance as elephants．This means researchers could use the discovery to develop new treatments that can help stop cancers from spreading or even developing in the first place．
"Nature has already figured out how to prevent cancer，"said Joshua Schiffman，an oncologist at the School of Medicine，University of Utah，US．
"It's up to us to learn how different animals tackle（对付）the problem so we can use those strategies to prevent cancer in people．"
4．Why are elephants unlikely to develop cancer？B
A．They have a large body size
B．They carry many genes that keep tumors from developing
C．Certain genes in their body kill existing tumors
D．Their genes suffer no DNA damage
5．According to Dr．Vincent Lynch，what has been a risk in the evolution of large animals？D
A．Extreme weather
B．Cells killing themselves
C．Human behavior
D．A risk of deadly tumors
6．What does the underlined expression"this phenomenon"on the sixth paragraph refer to？A
A．The risk of cancer is not related to body size
B．Larger animals have protection from TP53
C．Larger animals suffer the same risk of cancer as smaller ones do
D．The larger animals are，the bigger risk of cancer they have
7．We can conclude from the last three paragraphs thatB．
A．depending on nature is not enough to fight against cancer
B．the TP53genes have proven useful in stopping cancer in mice
C．this new treatment is more effective than the present ones
D．humans are expected to stop cancer in the near future．
分析 本文属于说明文阅读，作者通过这篇文章向我们介绍了大象为何很少患癌症的原因，这对人类治疗肿瘤有非常重要的意义．
解答 4．B 细节理解题，根据第三段A team at the University of Chicago，Us has found that elephants carry a large number of genes that stop tumors（肿瘤）from developing可知美国芝加哥大学的一个团队发现，大象携带大量的基因，阻止肿瘤的发展，可知大象不得癌症是因为本身具有的基因的原因，故选B．
5．D 细节理解题，根据第五段If every living cell has the same chance of becoming cancerous，large creatures with long life spans like whales and elephants should have a greater risk of developing cancer than humans and mice do可知如果每一个活细胞都有相同的机会成为癌变，大型动物寿命长像鲸鱼和大象应该有一个更大的比人类和老鼠患癌症的风险，由此可知体型大的动物具有得癌症的更大肿瘤，故选D．
6．A 细节理解题，根据第五段But across species，the risk of cancer does not show a connection with body mass．可知跨物种，罹患癌症的风险并不与身体质量有关，this phenomenon指的是这种现象，故选A．
7．B 推理判断题，根据倒数第三段The study also found that when the same genes were brought to life in mice，they had the same cancer resistance as elephants可知研究还发现，当相同的基因被带到老鼠身上，他们和大象一样可以抗癌症，故选B．
点评 考查学生的细节理解和推理判断能力．做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确选择．在做推理判断题时不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
