17．Scientists have overcome a major difficulty for humans to receive life-saving organ transplants from pigs，thanks to a powerful new gene-editing technique．
In a paper in the US journal Science，the researchers described using gene-editing method to remove potentially harmful DNA sequences at 62locations，which are the remnants（留存之處） of a virus called PERV，from the pig genome．
Globally human organs for transplant being short in supply，researchers and doctors have long hoped that the problem could be solved through the availability of suitable animal organs for transplant，a concept known as xenotransplantation．
Pigs have been especially promising candidates due to their similar size and biological structure to humans．
But one of the largest safety concerns has been the fact that pigs，similar to most mammals，contain PERVs in all their living cells-that are harmless to their native hosts but can cause disease in other species．
"PERVs and the lack of ability to remove them from pig DNA was a real barrier on the promising stage set for xenotransplantation．"
In the new study，scientists made 62genetic edits to inactivate viruses in pig cells，which they called"an explosive leap forward"．
When these cells were then introduced to human cells in the lab，PERV infectivity was reduced by up to one thousand fold，they said．
"Our work got away the shadow PERVs put above the field more than a decade ago when the virus was discovered，while renewing our faith in xenotransplantation，"lead author Luhan Yang，a post-doctoral fellow at the Harvard University，said．
The team hopes eventually they can completely root out the risk that PERVs could cause disease in xenotransplantation by using modified pig cells to clone a line of pigs that would have their PERV genes inactivated．"We still have a long way to go，though．"Luhan added．

33．From the passage，we may know thatD．
A．PERV is found during Luhan Yang's experiments
B．PERV infecting rate has been reduced to 1‰now
C．the breakthrough is the result of a decade-long project
D．PERV is not a threat to same species in organ transplantation
34．Which of the following is TRUE？C
A．Explosive materials are used in experiments．
B．Experiments are carried out in 62locations in US．
C．Further research is still needed in Xenotransplantation．
D．Gene-editing method is used to remove harmful pig organs．
35．Which would be the best title for the passage？D
A．A big breakthrough in scientific field．
B．Viruses in pig cells are inactivated．
C．Viruses are defeated by scientists．
D．New hope in xenotransplantation．

分析 本文主要講述了在器官移植方面需要克服的一個病毒問題，但是隨著科學研究的進展，異種移植是有可能成為現(xiàn)實的．

解答 33．D 細節(jié)題．根據(jù)文章內容，the researchers described using gene-editing method to remove potentially harmful DNA sequences at 62locations，which are the remnants（留存之處） of a virus called PERV，from the pig genome…Pigs have been especially promising candidates due to their similar size and biological structure to humans由此可知，科學家已經(jīng)使用了一種新的基因剪輯方式來移除病毒PERV，它對于同種類型的器官移植已不在是威脅，結合選項，故選D
34．C 推理題．根據(jù)文章內容，The team hopes eventually they can completely root out the risk that PERVs could cause disease in xenotransplantation by using modified pig cells to clone a line of pigs that would have their PERV inactivated．"We still have a long way to go，though．"Luhan added．研究團隊希望以后能夠用現(xiàn)代的豬身上的細胞來克隆出相應的使用在異種移植上．在這條路上，需要走的路還長，還有許多的工作需要做，結合選項，故選C
35．D 主旨題．根據(jù)文章內容，主要講述了在器官移植方面需要克服的一個病毒問題，但是隨著科學研究的進展，異種移植是有可能成為現(xiàn)實的．結合選項，故選D

點評 本文是一個科教類閱讀理解，題目涉及多道細節(jié)理解題，做題時結合原文和題目有針對性的找出相關語句進行仔細分析，結合選項選出正確答案．推理判斷題也是要在抓住關鍵句子的基礎上合理的分析才能得出正確答案，切忌胡亂猜測，一定要做到有理有據(jù)．

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