Which two of these are characteristics of the 802.1Q protocol?（） [" it is a layer 2 messaging protocol which maintains vlan configurations across network."," it includes an 8-bit field which specifies the priority of a frame."," it is used exclusively for tagging vlan frames and dose not address network reconvergence following switched network topology changes."," it modifies the 802.3 frame header,and thus requires that the FCS be recomputed."," it is a trunking protocol capable of carring untagged frames."]
规定期限内，对配额以内的商品征收最惠国税，超过配额征收普通税甚至罚款，这种非关税措施叫做（） ["全球关税配额","国别关税配额","关税配额","非优惠关税配额"]
班级授课制
What is the purpose of Dual Ring Interconnect with D C for SDH rings？（） ["Protects signals when a ring switch fails","Protects signals when multiple span switches fail","Protects pre-emptible traffic from being dropped when a ring switch occurs","Protects signals against any combination of link failure in each ring"]
当今世界的经济趋势是什么？
沉降速度
