Which two of these are characteristics of the 802.1Q protocol?（）

• A、it is a layer 2 messaging protocol which maintains vlan configurations across network.
• B、it includes an 8-bit field which specifies the priority of a frame.
• C、it is used exclusively for tagging vlan frames and dose not address network reconvergence following switched network topology changes.
• D、it modifies the 802.3 frame header,and thus requires that the FCS be recomputed.
• E、it is a trunking protocol capable of carring untagged frames.