Cellphonesareveryusefulandthey'regreatfun.Butcellphonesdohaverisks.Ifyouhaveone，itisnecessarytounderstandtheserisks，andlearn__11__enjoyyourphonesafely.__12__canbeawonderfulwaytokeepintouchwithyourfriends.Butbadpeoplecanalsosendmessages.Ifyoureceivearudeorterrifyingmessage，donotreplyorforward(转发)it.__13__， 　　savethemessageandshowittoyourteachersorparents.Ifyoureceiveamessagesayingthatyou__14__abigprize，don'tbelieveit.Sendingpicturesfromacellphoneisfast，easyandfun.Butmakesureyousendonlypicturesthatyouwouldn'tmindotherpeople__15__．Andyouaremorelikelytohaveanaccidentifyoutrytouseyourcellphonewhile__16__theroad.Therearecarsandbusestowatchoutfor！Hangupyourcellphone__17__youwalk.Withyourparents'help，youcankeepyourcellphone's__18__，youwon'thavetoworryaboutreceivingunwantedcallsormessages！Remembernottotalkonthecellphonetoooftenortoolong.Yourparentswillbe__19__ifyouspendtoomuchmoney.__20__yourcellphonewhenyousleep.Thesoundsofrubbishmessagesmaywakeyouup.(B)11.A.howB．howtoC．whatD．whatto(C)12.A.SendmessagesB．UsecellphonesC．SendingmessagesD．Us