问题：

[单选] Which of these statements best describes VPLS？（）

A .  Neither broadcast nor multicast traffic is ever flooded in VPLS.
B .  Multicast traffic is flooded but broadcast traffic is not flooded in VPLS.
C .  VPLS emulates an Ethernet switch， with each EMS being analogous to a VLAN.
D .  Because U-PE devices act as IEEE 802.1 devices， the VPLS core must use STP.
E .  When the provider experiences an outage， IP re-routing restores PW connectivity and MAC re-learning is needed.