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				31．We believe scientists will    a way to solve the problem  of air pollution．A．catch up with     B．come up with       C．put off          D．set off			【查看更多】
			


		
     
    


		
    
		
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    We believe scientists will ________ a way to solve the problem of air pollution．

    1. A.
      set off
    2. B.
      put off
    3. C.
      come up with
    4. D.
      catch up with
    

			
    
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