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  • 科目:英语
  • 题型:单选题
  • 难度:中等
  • 人气:1999

7.Although the causes of cancer ____, we do not yet have any practical way to prevent it.  

A.are being uncovered B.have been uncovering
C.are uncovering D.have uncovered
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7.Althoughthecausesofcancer,we