Question

4．People have been wondering why elephants do not develop cancer even though they have lifespans（寿命）that are similar to humans，living for around 50 to 70 years．
    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）developing．To be precise，they found 20 copies of an anti-tumor gene called TP53 in elephants．Most other species，including humans，only carry one copy．
    According to the research，the extra copies of the gene improved the animal's sensitivity to DNA damage，which lets the cells quickly kill themselves when damaged before they can go on to form deadly tumors．
"An increased risk of developing cancer has stood in the way of the evolution of large body sizes in many animals，"the study author Dr Vincent Lynch told The Guardian．If every living cell has the same chance of becoming cancerous（癌变的），large creatures with a long lifespan like whales and elephants should have a greater risk of developing cancer than humans and mice．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（悖论）"．Biologists believe it results from larger animals using protection that many smaller animals do not．In the elephant's case，the making of TP53 is 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 spreading or even developing in the first place．
"Nature has already figured out how to prevent cancer，"said Joshua Schiffman，a biologist at the School of Medicine，University of Utah，US．"It's up to us to learn how different animals deal with the problem so that we can use those strategies to prevent cancer in people．"
32．Why are elephants unlikely to develop cancer？D
A．They have a rather large body size．
B．Their genes suffer no DNA damage．
C．Certain genes in their body kill existing tumors．
D．They carry many genes to prevent tumors developing．
33．According to the passage，what has been a risk in the evolution of large animals？A
A．Deadly tumors．
B．The huge body mass．
C．Cells killing themselves．
D．Sensitivity to DNA damage．
34．What does the underlined part"This phenomenon"in Paragraph 5 probably refer to？B
A．Larger animals have protection from TP53．
B．The risk of cancer is not related to body size．
C．Larger animals suffer the same risk of cancer as smaller ones．
D．The larger animals are，the bigger risk of cancer they will have．
35．What can be concluded from the passage？C
A．Depending on nature is surely enough to fight against cancer．
B．The TP53 genes have proved useful in stopping cancer in people．
C．Humans are expected to prevent cancer with the making of TP53．
D．The extra copies of elephants'genes are used to cure cancer patients．

Answer 1

分析 本文主要介绍了在美国芝加哥大学的一个团队发现大象携带大量阻止肿瘤发展的基因．在动物的进化中肿瘤是极大威胁．而物种患癌症的几率和它们的体型没有关系．在大象的案例中，TP53的制作是让这个物种存活的自然方法．因此人们有望通过合成TP53来预防癌症．

解答 32．D推理判断题．根据第二段A team at the University of Chicago，US has found that elephants carry a large number of genes that stop tumors（肿瘤）developing．可知在美国芝加哥大学的一个团队发现大象携带大量阻止肿瘤发展的基因．故选D．
33．A推理判断题．根据第四段An increased risk of developing cancer has stood in the way of the evolution of large body sizes in many animals，可知在大体型的动物的进化中，患癌症的风险增加．由此可知，在进化中肿瘤是极大威胁．故选A．
34．B词义猜测题．根据第四段But across species，the risk of cancer does not show a connection with body mass．可知物种患癌症的几率和它们的体型没有关系．故选B．
35．C主旨大意题．根据最后一段"It's up to us to learn how different animals deal with the problem so that we can use those strategies to prevent cancer in people．"可知是时候了解不同的动物是如何处理这种问题，为了我们可以使用这些策略来预防癌症．而根据倒数第三段In the elephant's case，the making of TP53 is nature's way of keeping this species alive．可知在大象的案例中，TP53的制作是让这个物种存活的自然方法．由此推知，人们有望通过合成TP53来预防癌症．故选C．

点评 本文考察学生的理解推断能力以及细心程度，只要抓住文章的关键词，采用寻读的方法查找细节，就能找到正确答案．