Which protocol is a Cisco proprietary enhancement for 802.1d that allows separate spanning-tree instances for each VLAN?

A. IEEE 802.1w
B. PVST+
C. CST
D. RSTP

B. Per-VLAN Spanning Tree+ elects a root bridge for each VLAN and creates a topology table for each VLAN. It is a Cisco proprietary protocol due to the bridge ID calculation it must perform for each VLAN.