Since we have a focused subject ，we should not talk ________.
D
译文：既然我们已经有了命题，我们就不应漫无边际地交谈。此题考查对固定短语的掌握情况。atonce立刻;athand在附近，在手头，即将发生;atintervals间或，不时;atrandom随便，任意。
Directions:TranslatethefollowingparagraphintoChinese.
Cyberspace,ofcourse.isbiggerthanatelephonecall.Itencompassesthemillionsofpersonalcomputersconnectedbymodems-viathetelephonesystem-tocommercialonlineservices,aswellasthemillionsmorewithhigh-speedlinkstolocalareanetworks,officeE-mailsystemsandtheInternet.Itincludestherapidlyexpandingwirelessservices:microwavetowersthatcarrygreatquantitiesofcellularphonesanddatatraffic;communicationssatellitesstrunglikebeadsinthegeosynchronousorbit;low-flyingsatellitesthatwillsooncrisscrosstheglobelikeangrybees,connectingfolkstoofar–flungortoomuchonthegotobetetheredbywires.Somedayevenourtelevisionsetsmaybepartofcyberspace,transformedintointeractive“teleputers-calledfull-servicenetworksliketheonesseveralcable-TV”bysocompanies(includingTimeWarner)arebuildingalongtheoldcablelines,usingfiberopticsandhigh-speedswitches.