![Millionsofaircrafttakeoffaroundtheworldeveryyear.Theski...]( "Millionsofaircrafttakeoffaroundtheworldeveryyear.Theski...")
- 问题详情：Millionsofaircrafttakeoffaroundtheworldeveryyear.Theskiestheyflyinseemlimitless-milesofemptyspace.But,withthenumberofflightsincreasingeachyear,thisemptinessnolongerexists.Researchersintheworldofaviation（航空）areworriedabouttheincreasingpressure...
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