whAt ArE thE mAin FunCtions oF A FirEwAll systEmA、it protECtED pACkEts oF inFormAtion From BEing rAiDED、B、it CAn BrEAk EvErything up into littlE pACkEts.C、it CAn mEEt thE worlD DEmAnD oF thE gEnEriC plug-in CArD、