A. IEEE 802.1s （MST）
B. IEEE 802.1Q （CST）
C. Cisco PVST+
D. IEEE 802.1d （STP）
E. None of the other alternatives apply

A. To enhance Spanning Tree troubleshooting on multilayer switches
B. To reduce the total number of spanning tree instances necessary for a particular topology 
C. To provide faster convergence when topology changes occur in a switched network
D. To provide protection for STP when a link is unidirectional and BPDUs are being sent but not  received
E. None of the other alternatives apply