问题：

[单选] You are about to migrate a customer network to use a VSS. Which of these statements is true about a VSS？ （）

A .  The VSS switch must be the root bridge for all VLANs and is automatically designated
B .  The VSS switch is defined in RFC 4318 as a managed object
C .  The PAgP+ or LACP protocols are used to maintain the operational state of the VSS devices
D .  A VSS interoperates with a virtual port channel
E .  The 802.1Q or ISL protocols are used to maintain the operational state of the VSS devices
F .  A VSS increases the size of the spanning-tree domai