单项选择题
Whatisastaticpacket－filteringfirewallusedfor？（）
A.Itvalidatesthefactthatapacketiseitheraconnectionrequestoradatapacketbelongingtoa
B.Itevaluatesnetworkpacketsforvaliddataattheapplicationlayerbeforeallowingconnections
C.Itanalyzesnetworktrafficatthenetworkandtransportprotocollayers
D.Itkeepstrackoftheactualcommunicationprocessthroughtheuseofastatetable
