简介:你知道什么叫“温室效应”吗?它对地球又有什么样的影响呢?Agreenhouseisabuildingmadeofglasswhichisusedforkeepingoolplantswarmwhentheoutsidetemperatureislow.Inasimilarwaythereareseveralgasesintheatmospherewhichtraptheheatproducedbythesunandpreventitfromescaping.Thesegasesareknownas“greenhousegases”,andthewayinwhichtheytrapheatintheatmosphereiscalled“thegreenhouseeffect”.Thisisnotsimpleairpollution.Mostofthemaingreenhousegasesexistnaturallyinsmallamountsino...
简介:看完电视节目之后,观众可以马上反馈信息。这种双向的电视交流已不再是梦想。Communicationbytelevisionhasbeenone-waysinceitsbeginning.Howev-er,thetelevisionwatcherwillsoonbeabletotalkback.Two-waytelevisionisnowapossibility,makingelectroniccom-municationagoalforthefuture.Becauseofcomputersandcabletelevision,theaudiencewillsoonbemorethanwatchers.Theywillbeabletodomorethanchoosetheirprograms.Theywillalsobeabletogivefeedbackonthem.Two-wayTVisnotadream.Thehard-warefors...