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 domain.