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  • 科目:英语
  • 题型:单选题
  • 难度:中等
  • 人气:1373

It has been proved ____ several new kinds of medicine____ a positive effect on the cure of H7N9.

A.which,has B.if, has
C.that, have D.what, have
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Ithasbeenprovedseveralnewkinds