Acknowledgements, sequencing, and flow control are characteristics of which OSI layer?（）

A.By default， all defined VLANs are allowed on the trunk.
B.Each single VLAN， or VLAN range， must be specified with the switchport mode command.
C.Each single VLAN， or VLAN range， must be specified with the vtp domain command.
D.Each single VLAN， or VLAN range， must be specified with the vlan database command.

A.It is supplied by the CSU/DSU.
B.It is supplied by the far end router.
C.It is determined by the clock rate command.
D.It is supplied by the Layer 1 bit stream timing.

A.A WPA key is longer and requires more special characters than the WEP key.
B.The access point and the client are manually configured with different WPA key values.
C.WPA key values remain the same until the client configuration is changed.
D.The values of WPA keys can change dynamically while the system is used.